Would an E9 comply if ordered to attention by an O1?

Yes as to it being professional, but never should someone brand new need to command someone who has been in for so long to attention, that is more abuse to power. Any enlisted will know to respect an officer, and will help guide them through their knowledge as a professional.

I knew an Lt that when asked a question about senior NCO'' needing to salute.. the Lt replied they do it outta courtesy and that they wouldn't want to piss of one...

I dont believe I've ever seen an O-1 stupid enough to do that l.

Nothing would happen

Yes the E9 is required to but at the same time the 2LT needs to respect that E9 because that E9 had earned his or her place and respect.

In front of juniors, he would. The knife hands would come out later.

As per the UCMJ he would have to, since technically a superior officer gave him an order. BUT! As an E-9, he/she has ridiculous authority and that O-1 wI'll definitely learn their place and the never fuck with an E-9 ever again lol

I would obey the order but I would explain the facts of life to him while at attention
Did twice shortly before retirement. 2 different enswines

Yes, but the lt would be schooled afterwards