If it really is a draft, a thin light ribbon will work. Something
like the old Christmas tree tinsel. Tape it to the end of a stick.
If you can't find anything like that, cut a thin strip of the thinnest
paper you can find. The end will usually flutter.

A puff of baby powder can work too. Sometimes the can will puff a bit
out when you squeeze it.

Very likely it is not a draft. Are you near a window? It is common
to feel radiative heat loss from your warm body to a cold surface, and
think it is air movement when it is really not.