For Navalny? Putin is shooting him down because he's gaining too much popular support exposing and fighting corruption. They don't want people on the streets supporting him.
In general, follow the money trail (or the power trail) and it's easy to see who's censoring stuff. Maybe not very obvious in other countries, but in Russia it's clear as day. In Russia-wide issues the power trail always terminates at Putin, with local issues it could be some local government official.
Unfortunately in the general case it is usually very difficult to follow the money and power trail - and one needs to first identify that there is censorship (or coercive information) to begin with. In Russia, there are many actors - the US and Western allies have a lot of interests (both monied and power) there as well - as does China.
Not sure exactly what I was expecting you to say about the general case, but thank you.
