Student or Learner
a. I don't know if some of my friends will be at the party.
Does that mean
1. I don't know if any of them will be at the party. (maybe none of them will be at the party and maybe some of them will)
2. As regards certain of my friends, I don't know if they will be at the party. (I know Tom, Pete and Harry will be there, but I do not know if Jack, Robert and Ed will be there or not)
I think (a) is ambiguous. I might have specific friends in mind and I might not.
I am not a teacher.
It is ambiguous as a written sentence. In normal speech, intonation should make clear what you mean.