Can fluid get in inner ears like it can in middle ear? if so, how does dr diagnose inner ear fluid.

Middle vs inner?: Not sure what you mean here. The ear canal is open to the outside, so every time you bath, shower, swim, are in the rain, etc, fluid can enter the ear canal.The tympanic membrane[tm]) ear drum, stops any fluid from getting into the inner ear (which some people may call the middle ear). Using an otoscope, a dr. Can tell with reasonable certainty if "fluid" is behind the tm, and decide any tx needs.