Using the description of Rope Trick as a guide, it seems to me that Locate Object wouldn't work. The passage reads:
"Creatures in the extradimensional space are hidden, beyond the reach of spells (including divinations), unless those spells work across planes."
Locate Object has nothing in its description that indicates it works across planes, and in fact has a defined range limit. I would say you could use Locate Object against the Bag of Holding itself, since it is on the plane...in the same way that you can Dispel a Rope Trick's planar interface (the "window" that people pass through to get in and out), but you can't Dispel things within the Rope Trick.