How many wheel does a train have?

Depends how many wagons or carriages the train has.

A goods wagon can have 4 wheels, but 8 is more usual, 4 on each of 2 bogies.

A passenger carriage normally has 8, 4 on each of 2 bogies.

A locomotive has 8 or 12, 4 or 6 on each of 2 bogies.

Then multiply by the number of vehicles in the train.

For example, a 12-car passenger train has 96 wheels.

Other arrangements are possible, where a bogie of 4 wheels is shared between two adjoining carriages, for example on French TGV high speed trains. This gives greater stability at high speeds.