b. adverb clause
Only one of the sentences contain an adverbial clause. I lay out the explanations below.
(A) NO ADVERBIAL CLAUSE. "Where I could get some coffee" is part of a reported speech.
(B) NO ADVERBIAL CLAUSE. "What she pointed out" is a noun clause.
(C) NO ADVERBIAL CLAUSE. "How to invest my money" is the direct object of know; hence, it's a noun clause.
(D) "Where they can find food easily" is an example of an adverbial clause. It is an adverb of place, answering the question: Where do most animals thrive?