nunc quam rem vitio dent quaeso animum adtendite
= now I ask you to look at the thing they criticise [him, the poet of the earlier part, for]
(aliquid alicui vitio dare: impute something to someone as a vice/crime etc.)
qui utramvis recte norit ambas noverit
= who knows one [play] knows both [not Terence, but anyone]
Faciuntne intellegendo ut nihil intellegant?
= As for understanding, don’t they behave as if they understood nothing?
[although I think that “–ne” should strictly be neutral, but here it seems he has bent that rule]
de(h)inc ut quiescant porro moneo et desinant
= hence/so [in logic] I advise that henceforth they cease and desist their abuse
Hope some of this is useful.
Keep up the good work!