How may pi-bonds are there in Ammonium molecule?

The figure below shows the structure of ammonia molecule and that of ammonium ion.  Single bonds do not contain π bonds.  As both ammonia molecule and ammonium ion has N-H single bonds only, there is no π bond in each species.

First, ammonium is an ion not a molecule. It has the formula NH4+. Each H atom is bound to the central N atom by a single bond. Thus, there are no pi bonds in an ammonium ion.