The most surefire way would be to put a device between your router and your ONT/modem to capture the packets and see what requests are being sent. It's not complicated but it IS a lot of information to sift through.

Your router may have the ability to log requests, but many don't, and even if yours does, if you're concerned the device may be compromised, how can you trust the logs?

BUT, with all that said, these attacks are typically not very sophisticated. Most of the time they're searching for routers at 192.168.1.1 with admin/admin as the login credentials. If you have anything else set, you're probably good from 97% of attackers (This number is entirely made up, but seriously that percentage is high). You can also check for security advisories on your model of router. If you find anything that allows remote access, assume you're compromised.

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As a final note, it's more likely these days that the devices running these bots are IoT devices and web browsers with malicious javascript running.