Recently, I had a scheduled task running for long, and i noticed I couldn't find the logs as I used to find them while using DSM 6. I ended up creating a ticket for Synology Support, but I did get too far with them. I started looked at the running processes, and with a bit of luck I was able to find it. the location in my NAS is /volume#/@tmp/synoscheduler/logs It happens to be the case it's the same volume I write the logs to (once the tasks finished). For you it may be volume1 or else Inside you will find a folder with a name starting with @, like @16589, once you have a task running.
A throwback from 2012, when we used to live in a basement apartment from the 60s-70s in Laval, QC. To be fair it didn't feel so dusty, but the air purifier told another story (this is after ~ about 4 months of use) yuck! All cleaned up and ready to use again!