How can I phrase questions to user tests to not give away the solution?

Phrase tasks from the participants perspective not knowing about the IA of the application/site.

From https://www.nngroup.com/articles/better-usability-tasks/:

Task goal: Use the location finder tool (labeled Find a Branch)

Leading user task: Find a branch near you and see when it is open tomorrow.

Improvement: When is the bank location that’s most convenient to you open tomorrow?

When it is difficult find good tasks, create a story for each task that deals with the reason why the feature exists:

You need to open a new account for your business tomorrow and don't want to invest too much time in that. When is the bank location that’s most convenient to you open tomorrow?

Say if it's a travel site, tell them to book a flight and a hotel.

Just give them the final objectives.

And then tell them to "think aloud" ( not what they think about xyz, but "I am pressing the red button")

If you want to ask questions as you go along you end up asking mangled English "why did you press the 'thing,' you just pressed"

You can't call the thing by what it does because that gives the game away.

Start by asking them to think out loud.

Then keep the monologue going:

• Tell me what you are seeing on the screen
• Tell me what do you think that thing that you are seeing does etc.

You can find out more here.

As a general rule, try to avoid using the labels for your sections. I've found that testers use your wording as a guide and focus on searching that word in the labels instead of doing the mental work of guessing where to find it.

To avoid this, describe things you can do inside the section, or content it might contain that would be beneficial for the user to find. Don't use synonyms since users can quickly figure those out as well.