There are, again, two matters here:
"Beyond the Jordan"
Note the succinct statement of Ellicott -
Beyond Jordan.—It is disputed whether this means on the east or on the
west of the Jordan. It is certain that the route taken by Joseph lay
to the east of the Dead Sea; for Goren-Atad is placed by Jerome at
Beth-Hoglah, which lay between the Jordan and Jericho, and Joseph
could have gone thither only by travelling through the territories of
Moab and Amnion. [He says much more about this but is inconclusive.]
Cambridge Bible for Schools and Colleges offers this -
- the threshing-floor of Atad] Goren-ha-Atad, a threshing-floor of “the thornbush,” or “bramble” (Jdg 9:14-15). The place is nowhere else
Ellicott makes this helpful remark -
(10) Threshingfloor of Atad.—Atad means “a thorn-bush,” the rhamnus
paliurus of Linnaeus, translated “bramble” in Judges 9:14. As
agriculture was only beginning to be practised in Canaan, this
threshing. floor would be common property, situated in some place easy
of access, and probably a village would grow up near it.
Therefore, the short answer to the question - we do not know.