'zpool status' will tell you the last time a scrub was run, or if one is running currently and information about it. Then check your crons and see that they make sense and match what you see with zpool status.

Well it is not every week.

> scan: scrub repaired 0 in 0h36m with 0 errors on Sun Aug 12 06:00:50 2018

I don't see any cron jobs though...

Given the speed of that, I'd bet you don't have a huge pool (or if you do, that's a really nice speed). I'd bet someone's doing it manually. That's what I do for my own systems (about once a month) since they're not heavy use (personal and parent's file servers).