Unfortunately, BG1 doesn't show you the charges on your wands. In general, wands you find have 1-10 charges, and merchants will
usually put ~25 charges on them if you sell and then buy them back. One notable exception is the proprietor of the Friendly Arm Inn, who will put 50 charges on your wands. If you want to know the exact number of charges, you'll have to use something like
GateKeeper to look at your savegames.