Verified answer

We say:

Je ne sais quoi faire, instead of je ne sais pas quoi faire, which is equally right.

Je ne sais quoi dire= don't know what to say.

With quoi, qui, we can ommit pas.

With some pronouns, we might ommit pas. Je ne sais lequel manger=don't know which one to eat.

But we might not, as well. But in nowadays french, we ommit them there.

Ciao...John-John.-

no not necessarily when "lequel" is used in a negative sentence whenever you use i don't know or i can't just like you use the apostophe instead of the word "not" you can omit the word "pas" in the translation ex: i couldn't tell you "je n'ai pu te le dire" i don't know what to do" "je ne sais quoi faire"

John John is right.

In reality, most of time it depends of the person who speaks : without "pas' is more "bourgeois", just a question of style.