Questions & Answers about Non so se Marta può venire al bar alle otto.
Here se means if or whether.
In this sentence, it introduces an indirect yes/no question:
This is very common in Italian:
- Non so se è vero. = I don’t know if it’s true.
- Mi chiedo se arriva oggi. = I wonder whether he/she is arriving today.
So this se is not about a condition like If it rains, I’ll stay home only; it can also mean whether.