Focussing the attention on the source of mind and remaining there is self-enquiry.
When mind strays due to the influence of tendencies we have to bring it back~that is
self-enquiry.
Self-Enquiry is not a thought but paying attention to the source of it.
There is no ego apart from the idea of it.
"I" thought arises from the self and depends on the self for it's existence.
It is never apart from the self and infact the self but forgetful of it's true nature.
So ego is only a thought,an aberration on pure self.
It believes in the lie o it's own independent existence.