They’re going to offer feedback, but if they don’t know what you want, it may not be as useful as you’d like. Make it easy on them. Give a list of questions at the end, or at the end of chapters/scenes. Some things are going to be specific about the story, but a lot will be general story craft questions, so …

Ask what they like about the story first, then …

Give them a list of the things that construct the story:

Does the place the story is set in make sense? Can you see it, feel it, be in that world as you travel through the story? Is it clear in the mind, either visually or through other senses?

That’s setting.

It’s about the geography and location, but also the period (era, time, season, weather, etc.) so be specific in how you word the question, especially if there are differences between what a person would know in this world, and how that world is set against it (a little of what they know can help bring the whole world to life).
It’s also about descriptions of place, the mood and atmosphere created by the descriptions (as the character experiences things). It’s about the social interactions and rules (speech mannerisms, politics, money, trade, etc.). And names – are the names appropriate for the genre, setting, and theme? Are the names convincing and believable for this world?

Do the actions and events of the character make sense, do you believe he’d do the things he does, did you cheer him on, fear for him, at every turn, etc.?

That’s plot.

It’s about the actions that demonstrate the journey, including the character arc changes demonstrated through responses to the physical, external events.
Did you feel his plight right from the beginning, or was there a lot of stuff that didn’t need to be there, or maybe there wasn’t enough stuff to make him interesting?
Were there any places that didn’t work. Maybe you stopped reading, or asked how it mattered to the story or the main character. Was anything confusing? Did you understand why things happened and what he did when they happened?
Did you feel that the story resolved well, that the ending answered your questions and left you feeling fulfilled?
Was there anything that needed more explanation or demonstration to enhance your experience?

Were the conflicts obvious and relatable?

Talkin’ about Conflict

(with associated Tension and Suspense created in the reader)
There are usually two levels of conflict: external (the visible events and actions and obstacles, the physical movements and actions, the visible and viewable moments that play out like a movie in the reader’s mind) and internal (the struggle with self, whether with a purpose, or want, or a need). It’s about the mental/moral conflicts that are deflected by desires incompatible with the aims and goals, and self-perception, of the character.
The big issue for a story is emotional conflict. This is what drags a reader deep into the character, especially if it’s something they know from their own lives. These conflicts are shown through action, dialogue, values, and the transformation undertaken in order to achieve resolution. And it’s closely associated with the next section.

Did the story feel real? Were there any problems understanding who the characters were and why they did that they did? Were their motivations believable and appropriate?

That’s Character.

Everything in a story is really about the character. What’s the point of an action movie if there’s no person doing the action, and doing it for a reason? Character is what keeps readers interested. It’s them, but from a distance. Safe, while they undertake something dangerous.

And I know a lot of people try it, but a story needs more than one person. There needs to be at least one foil, or one antagonist, or one other character to test the main character against. Otherwise, it’s an introspective soliloquy. And I don’t know about you, but I tend to leave the room when someone talks about themselves for more than a minute or two. And having another character can demonstrate the paradoxes of life.

Would you know which character was speaking if there were no dialogue tags?

Dialogue is Character.

Dialogue is unique to the character, their history, their setting, their personality, their backstory. They are a result of cultural and political and social structures, and even if two people grow up in the same town, go to the same school, and have the same friends, they will not sound the same. There will be differences in tone, in beliefs, in the shape of speaking. Dialect isn’t what it’s about. Try speech, rhythm, musicality, word use. Some people like to get right to the point, some people like to avoid the crux of the matter, some people don’t say what they mean, and some people do, and their bluntness can offend others. Oh, yes, and men and women don’t use the same choices when speaking. They’re speaking the same language, but are shaped by their past, their family, their friends, their future.
Make sure they’re unique in how they sound, and how they think.

Is it clear who is speaking, thinking, doing?

That’s about POV (Point of View, or Perspective)

If it’s difficult for the reader to understand who is talking, thinking, doing, or too many of these things happen in the same paragraph, it’s going to stop them reading – because they won’t understand, or they’ll have to reread the section to try to get a handle on these things, and they may get it wrong. Long paragraphs aren’t good. Too short is likely not any better. But follow a few simple rules to make it easy on the reader (and I don’t think it matters whether it’s called omniscient, first, or third).
A general rule of thumb re paragraphing and dialogue:
The issue with the paragraphing is often about confusion with the who’s doing/saying what. The big one is the pronoun confusion. To make it easy on the reader, try this:
Talking, thinking, doing:
If it’s the same person, it’s the same paragraph.
If it’s a new person, it’s a new paragraph.
That means if one person is talking, there is no description of what another person is doing in the same paragraph as the dialogue. The talker can show internal thoughts if they’re the POV character, but if the speaker isn’t the POV character, there are actions, or action tags for them, but not internals. The POV character gets a new paragraph to either respond to or interpret the actions. Generally, this makes it easier on the reader.
And don’t, please don’t, put the thoughts or dialogue of two different characters in the same paragraph. Please.

***

That’s the start of the idea of what to ask a beta reader so you can make the story as good as it can be for other readers. It’s by no means the whole deal, only the basics. Have some specific questions ready, especially what the story is ‘about’, like theme or purpose. Be subtle, so they don’t necessarily know that’s what you’re asking. Let them make their own decisions about what’s important in the story, and you may find your eyes being widened.

And you may have noticed how closely these questions align with the craft skills. Readers are savvy. They understand. Trust them.