What is an example of "where" in an adverb clause?

[1] [Where I'm going] is none of your business.

[2] No one knows [where he is].

[3] It's interesting [where these things have come from].

[4] This is [where I want to be].

[5] This is the park [where we first met].

[6] She was surprised by [where I had gotten the magazine].

The bracketed expressions in [1] [2] and [6] are subordinate interrogative clauses (embedded questions) functioning respectively as subject, complement of "know", and complement of "by".

[3] is an extrapostion construction in which the subordinate clause is an extraposed subject. The basic non-extraposed equivalent is "Where these things have come from is interesting", where the subordinate clause is an interrogative.

[4] is a fused relative construction in which "where I want to be" is a noun phrase as subjective predicative complement of "be".

[5] is a relative clause modifying "park".

Note that in [5] "where" functions as an adjunct (your adverbial) of place in the relative clause, though it's a PP, not a clause.

Incidentally, I would strongly recommend dropping the term 'noun clause'. The classification of finite subordinate clauses is based on their internal form rather than spurious analogies with the parts of speech.