There is no direct way to find out which validator is running which client.
Some validators will use the default graffiti from their client and that graffiti will include the name of the client. You can tell by looking at some of the recent blocks. Check out in the graffiti column. That's probably one of the best way to figure it out. A graffiti can be anything and someone can choose any graffiti so it's not fool proof.
The second best way to figure out which client is used by a validator is with Michael Sproul blockprint project. It is not foolproof and it comes with some uncertainty but it will analyse how the blocks were constructed and come up with the best guest on which client did that block construction.
A good chart and resources on client diversity can be found on https://clientdiversity.org/. That website uses the blockprint project as one of its sources.