If a flow caRd get abandoned or defy where does it goes?

It gets banished — Flow's "then banish it" replacement catches any way the spell leaves the Chain that its own execution didn't cause (FAQ #11738).

When you counter a Flow spell with Defy or Abandon, the counter tries to move it off the Chain (to trash or back to hand), but Flow's delayed replacement (Rule 829.1.b.1) kicks in and sends it to the Banishment zone instead. This applies no matter which counter effect is used — even Abandon's "return to hand" is treated as leaving the Chain for Flow's purposes, so the spell ends up banished rather than in your hand or trash.