Could you tell me which sentence is right?:
"be at the right place at the right time"
"be in the right place at the right time"
and how can i answer the sentence "nice to meet you"??
Both of these sentences are correct. In English you can either be 'in' a place or 'at' a place and often both. The sentence is an expression and personally I don't think it is important which one you use.
The usual response to "nice to meet you" is "nice to meet you too".
Please click here for more examples of greetings.