If you can give up duality, Brahman alone remains, and you know yourself to be that Brahman, but to make this discovery continuous meditation is required. Don't allocate periods of time for this. Don't regard it as something you do when you sit with your eyes closed. This meditation has to be continuous. Do it while eating, walking and even talking. It has to be continued all the time.
Self-inquiry must be done continuously. It doesn't work if you regard it as a part-time activity.
You have to keep up the enquiry, 'To whom is this happening?' all the time. If you are having trouble remind yourself, 'This is just happening on the surface of my mind. I am not this mind or the wandering thoughts.' Then go back into enquiry 'Who am I?'.
If you can maintain the siege for long enough, a time will come when no more thoughts arise; or if they do, they will only be fleeting, undistracting images on the periphery of consciousness. In that thought-free state you will begin to experience yourself as consciousness, not as mind or body.