It's common in Indian English (especially in schools) to say "If you have any doubts, ask me now". As you might have guessed, the expression is understood to mean "If you did not understand something or if something is not clear to you, let me know and I'll explain again".
However, I believe the usage of "doubt" this way is incorrect in standard English. At the same time, I cannot think of a simple, conversational alternative to the expression.