In this case is my subordinate. The idea of doing the measurement was discussed with other people, I have 20+ years doing such debugging. I already had asked him to do the measurement.
My question started more to be sure he actually is going to do it, because I have experience with not doing what he is supposed to. Not a bad guy, but sometimes seems to just don’t understand.
I agree with the parent. When there is confusion like this, switch to open ended:
"OK, we both agree there appears to be a problem with the transmission. How do you propose we investigate?"
From the dialog it appears you were two steps ahead of the person and what he really needed was time to think it through. Asking the open ended question gives him space to think.
It makes sense to give a subordinate a directive. That he is a subordinate, however, doesn't mean a direct question will lead to effective communication.
I've worked with both types of managers - the ones that ask direct, pointed questions and the ones that ask open ended ones. I think the latter are more effective, but it really depends on the role (you don't want open ended discussions in emergencies).
For me, though, "We have problem X. What are the options for resolving it?" has a better chance at success than "We have a problem X. Can you look into Y?"
Btw: at the end the test confirmed the suspicion.