In order to find out if an object is charged or not, we can test it by using an electroscope.

1) When the object is touched with the metal cap of an electroscope, both the metal cap and the leaves acquire the charge due to conduction. As a result of

2) As a result of both, the leaves of the electroscope will have the same charge. It will cause the leaves to diverge showing that the object was charged, as shown in the pic: