Question

Where is oceanic crust thickest

Answer 1

The oceanic crust is thickest at mid-ocean ridges
Oceanic crust is the outermost layer of Earth's lithosphere that is found under the oceans and formed at spreading centers on oceanic ridges, which occur at divergent plate boundaries. It is about four miles thick and is composed of several layers, not including the overlying sediment.

Answer 2

The oceanic crust is thickest on the points that are the furthest away from the mid-ocean ridges. These makes the parts of the oceanic crust that are in close proximity of the subduction zones to be the thickest parts, pr in other words it comes as the thickest parts of the oceanic crust are the ones that are the closest to the zone of their destruction (or rather recycling).