Answer:
The subordinate clause is After he had waited an hour.
Step-by-step explanation:
A clause is a group of words that have a subject and a verb and that may be whether subordinate (when it does not express a complete thought, and it acts as an adjective, adverb or noun that modifies another clause) or independent (when it expresses a complete thought and it can stand alone as a sentence).
In the sentence provided, After he had waited an hour is the subordinate clause because it does not have a complete meaning on its own, and it has to depend in another clause in order to make sense. Likewise, it is also an adverb clause because it modifies or adds further information of WHEN Mr. Jones received a certain telephone call. On the other hand, the clause Mr. Jones received a telephone call directing him to go at once to a certain motel room is an independent clause because it expresses a complete thought on its own.