Answer:
Josh Richards is a musician whom I greatly respect.
Step-by-step explanation:
Whom is used when you're replacing an object.
Who is used when you're replacing a subject.
But what's the difference between a subject and an object? Basically, think of reversing the sentence:
- Josh Richards is a musician ___ I greatly respect.
- I greatly respect him. (Not "I greatly respect he.")
The subject of this sentence is I. The object, then, is him. So we must use whom.