What are lexical categories of “when” as in the sentence below? Conjunction?

She is homesick and uncertain when to go back to her home country."

Question

What are lexical categories of “when” as in the sentence below? Conjunction?

She is homesick and uncertain when to go back to her home country."

Answer

It is a "relative adverb" which gives additional information about her "uncertain" choice of time to go to her home country.