Is “which” a subordinating conjunction?

No, which is classified as a relative pronoun. Although a relative clause is a type of dependent clause, a relative pronoun is not the same as a subordinating conjunction because it acts as a subject/object or refers back to a noun, whereas a subordinating conjunction is a linking device.

It is also used as an interrogative word (e.g., “Which shirt looks best?”).

The QuillBot Grammar Checker can help ensure you’re using relative pronouns and interrogative words correctly.