Come back for the update:
At ORD:
-Checked in a large luggage and a guitar with a semi-hard case. I was recommended to gate check the guitar to avoid any mishandling at ORD (the luggage tag was printed out and attached to the guitar at check-in counter)
-brought on board a backpack, a carry-on, and an empty pool cue case (I managed to put the cues in the large luggage checked in)
At HKG the second day for PVG flight on KA (also in J):
-Bags were checked through all the way to PVG despite overnight connection (~23hr)
-Was stopped by the security check point officer and told I could not bring a hard cue case (empty or not) on board unless with explicit approval from KA to them
-->Went back to counter and the agent happily checked in the cue case
-->Upon arrival at PVG, the cue case had a inspection completed sticker by HKG security. Turns out an empty cue case with a piece of chalk in there was suspicious enough for HKG security