I’ve mentioned so-called “prepositions” at the end of sentences before, that they are okay because they are part of separable verbs. (A famous example: it’s okay to say “not put up with” rather than “up with which I will not put.”)
Here’s one that’s an actual preposition. Last sentence in the last panel:
The problem here is not just that it’s a preposition, but that it’s redundant. The sentence already mentions location with the word “where.”
So all you need to say is “Do you know where the crushed red pepper flakes are?”
When you’re talking about location, don’t end your sentence with “at.”