One way to determine if it is lacquer is to take lacquer thinner and rub the surface. If paint transfers to the rag, it is probably lacquer. You should be able to apply 2K primer over properly prepared lacquer. You run into problems when trying to apply lacquer over other types of coatings. If you're just needing to seal the sanded lacquer before painting, you may consider using epoxy. Spray two coats as a sealer, then top coat.
Hope this helps.
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