Question

Two charge are placed at a distance apart.Now if glass slab is inserted between them then the force between the charges the

Answer 1

Glass is not a good conductor of electricity or electric flux. But now a days glass (like your smartphone glass which have capacitive touch) are made in such a way that they can be used for conductive purpose.
So in your case if glass is purely insulator,then there will be no effect on charge and if it is conductive then those charge may attract or repel depending upon there polarity.

Answer 2

Glass is not a good conductor of electricity or electric flux. But now a days glass (like your smartphone glass which have capacitive touch) are made in such a way that they can be used for conductive purpose.
So in your case if glass is purely insulator,then there will be no effect on charge and if it is conductive then those charge may attract or repel depending upon there polarity.