Here are a few I can think of if you are asking for the first time:
- Are you free on Thursday at 10am? - What time on Thursday are free?
- How about Thursday at 10am? - Are you free any other time on Thursday?
- Can we speak on Thursday at 10am? - At what time can we speak then?
For confirmation (at least what I've heard):
- Is everything in order (as planned) for Thursday?
- Are we still okay on Thursday?
You could eventually write and ask him why he didn't reply:
- You didn't answer my email, I'm worried, so do we meet on Thursday at 10am or not?