I will tell you that I do not understand the Melodyne. But some time it helpful like when your vocalist does not believe he is a vocalist...
Is there dedicated Melodyne manual?
 
I have few questions.
1. If my vocal part is in A minor, why it wants to "snap to F minor"? If I select A minor on the left side of the screen, it let's me snap to A minor- is it what I supposed to do?
 
2. Is it only available two times per project? I used it twice, and then it would not load as regional effect. What is the work around?
 
3.If there is no work around- do I bounce (freeze) the track? So I freeze the track and it printed a clip that looks like stereo. It does not sound different, but it looks like it is a synth (2 waves) not as a mono vocal track. Is it normal? I need to know before I ruined all my vocal parts. Thank you very much.

When you bounce Melodyne (or AudioSnap or V-Vocal or other processed clip), the resulting wave file will match the interleave of the track. To make sure to get a mono bounce, make sure the track interleave is set to mono AND that you don't have any stereo effects in the FX bin that would coerce SONAR into switching the interleave.
 
No idea as to the other questions. Despite using Melodyne for nearly a decade I've never employed the snap function, so I wouldn't have even noticed if it had the key wrong.

1. Sounds like Melodyne for some reason isn't analyzing the right key - which algorithm is being used?  For a vocal track "Melodic" would normally be best.  
 
2. There's no hard limit AFAIK - I've had 3-4 instances at a time but never had a reason to test beyond that.   I'm assuming you're not trying to apply it more than once per unique clip?
 
3. Instead of Freeze, click on the end of the clip (or the Region FX pull-down menu) and choose Melodyne > Render Region FX.  You effectively want to bounce the clip itself, not the track. 
 

It can not tell the key at all. My vocalist is partially sings, partially talks, so it must be hard. I have it set to Interleave Stereo. But tonight I am using it on another track, also set to interleave stereo but it makes single wave (looks like mono). I don't think I had effects inserted.
 Ok, I think I know why: I used Freeze snow flake, and now using Render regional effect function. This is wgy it looks normal.
Thank you for replies.

Great!   At least you do have the render option working as needed.   One down...