Hi Joebenu & welcome to TAC!
If the label on your varnish says it is for use on acrylics, then it will be fine.
If you're talking about wood varnish (like the kind you would use on furniture or floors) then I would proceed with caution. Wood varnish can turn yellow over time, so you'd want a label that says it is non-yellowing, water-resistant, UV-resistant, and dries completely clear. I would do a test first by applying a coat on something (like a spare canvas) and seeing what happens.
If you can get a varnish that is specifically meant for use on acrylics, that's your best bet.
Hope this helps & good luck! :)
Hi Thaneeya, You have shared wonderful information here. It is the common problem of beginners but you provide a useful information when and how to use acrylic on varnish. Thanks for the info. Appreciable efforts,Keep it up.