What is it that is not changing?
There are many pointers to discovering "no I", and many approaches to unravel the knots coming from a belief in the thought "I".
Byron Katie's inquiry helps these knots to unravel and reveal what is with no beliefs and no "I". Douglas Harding's experiments helps us directly see it. And asking What/who am I? is yet another approach.
One that I find particularly helpful (although obviously not quite enough to have it "pop" completely), is asking What is it that is not changing?
Obviously, the only aspect of what is - right here/now - that is not changing, is the "ground" it all arises from, within and as. It is that which everything - awareness and phenomena alike - happens within and as.
I notice for myself that I find it, yet it seems somehow as subtly "other" because there is a subtle "I" as something else. Last fall, when it did pop, it just was - as everything else, with no "I" anywhere.