Final answer:
The word "often" in the sentence is an adverb that describes the frequency of the action being performed.
Step-by-step explanation:
In this sentence, the word "often" describes the frequency of the action being performed by your brother. Since it modifies a verb, it functions as an adverb.
Adverbs provide more information about verbs, adjectives, or other adverbs.
They often answer questions like how, when, where, why, or to what extent. In this case, "often" tells us how frequently your brother gets up at six o'clock to go jogging.
Learn more about Adverbs