Hello,
We have PPPOE server,
we need to check if any client in our network is using his router to send to another router.
maybe the routers are not mikrotik, any thing like tplink router
if he use his pppoe account on tplink router then he take dynamic ip from the tplink router to another tplink router and thats on ...
can we check that in the pppoe server ?
Thanks.

No it is not possible to check that, with any router.
You can only guess that because there is more traffic than you expect from a single customer.
But no technical way to know it.