Are these the keys that you were looking for?
The simple past tense indicates that the person has given up searching for the keys. The searching is in the past and over.
'Are these the keys that you've been looking for?'
The continuous past perfect tense implies that he has been searching and is still continuing to do so up to the point that you ask him this question.
? (By the way, can these two question marks be used together?)
You would punctuate your question:
I'd like to know if we could also say, "Are these the keys that you've been looking for?"
Your opening request "I'd like to know" is not written as a question (even though their might be a big question in your mind about whether or no you can. (lol)