How would you approach a Soldier wearing earrings on post that you couldn't identify as male or female?

"Excuse me, Soldier.....do you identify as female?"
"No, sir"
"Then why are you wearing earrings? You need to take them out."

It's easy! No earrings for ACU's period. If they are wearing them.. they are wrong.
If they are wearing ASU's and have earrings. Then they are females.
If they are wearing civvies and wearing earrings and you can't tell what their gender is, just be ambiguous about everything.

Depends on the uniform.

ACU: earrings are a no-go regardless.
ASU: gender should be apparent by the uniform
Civilian clothes: I would assume civilian and not apply military policy.

If there is some circumstance I have not yet imagined, I would give the benefit of the doubt and assume the soldier was in compliance (therefore female). I suspect addressing a male as "ma'am" may provide adequate resolution.