In asphalting, if we lay asphalt above a concrete pavement, do we need to apply tact coat first or not?

Yes. We need to apply tack coat to the substrate.

Yes we must apply Tact Coat other wise how joint will come goodbetween  concrete and asphalt

With tact coat is better because this will serve a good contact between asphalt and concrete and most important we have to consider the duration of the pavement. Without tact it is just fine but there will be no guarantee of life span.

Yes,we need to apply coat.

Tack coat/prime coat @ 0.60Kg/Sqm is must 

yes,so that it will contact properly and become strong

Yes we need a tact coat first. if we do not tact coat then concrete do not catch the asphalt so we fist tact the tact coat