independent noun, in compounds
What is a skill? It's something you can do, and do quite well. It is a technique that you can make happen with ease.
Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word: You do your technique on a bad guy, coming at you. You flip him over and knock him out. He was (わざ) a threat, but now he's not. You look closer at the bad guy. Turns out it's Woz, the Apple Co-founder. He was just trying to hand you an iPhone12, not grab your wrist. Whoops!
You've mastered tricky art like that one, have you?
Is Koichi teaching Nikka a new trick?
In judo, technique is more important than strength.