する verb
はんだんする
聞いたことから判断すると、真打ちは最後にあるようだね。
Judging from what I’ve heard, the best seems to have been saved for last.
判断 is judgement. Make that into a verb and you have to judge.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. It will help to know 判断 before learning this, but if you don't I won't judge you (the Crabigator will).