How to Know What Has Caused Conductive Hearing Loss?

I have mixed hearing loss and unilateral tinnitus. Most of my hearing loss is SNHL but also conductive. My doctor said there is nothing I can do. He has only seen audiogram and had a little look in the ears.

I would like to know the cause of the conductive hearing loss. Is there a scan like a CT or MRI that would help diagnose it? Or can they send a scope in?

Is my tinnitus more likely to be as a result of sensorineural hearing loss or conductive hearing loss?

My doctor doesn’t seem to know much about tinnitus.