IN A SENTENCE:
He felt that she knew where he was going, but she never protested nor gave any sign of disapproval.

the part starting from "but" till the end denotes what type of a clause?

Your use of 'never protested' suggests you are learning American, so I will discount myself from responding.

it's not a clause. this is two complete sentences linked together with a conjunction "but."

Say what? There are some glaring errors in your response that seem to disqualify you from answering any questions on English grammar.

e.g. "I never protested the decision to increase the tax." How does the use of "never protested" imply that I'm "learning American?" That's absolutely ludicrous.
Which is a nice segue into your second puzzling comment.

What is "learning American"? Do you mean "learning English"? "American" is a nationality, "English" is a language.
That, my friend, seems to be the giveaway that you are ESL--English as a Second Language.