Thank you sir! @Kou Hayakawa

SDS-PAGE is a simple way, as long as there is enough enzyme to detect it. An activity assay is another way to do it.

By the way, a good way to get rid of all the enzyme is to pass the sample through an ultrafiltration membrane with a suitable molecular weight cutoff. Small peptides pass through and the enzyme gets left behind.

If you boil the sample after the reaction, the enzyme may coagulate, allowing you to remove it by centrifugation.