This is a relative pronoun that relativizes inanimates. In the fourth sentence of the Babel text
ē teteñ ien hēja ñanna jamāonre nīkan jakōnōr ja ñi jōl rā anīstīli;
ja relativizes jakōnōr. ñi jōl rā anīstīli is “make the top of it to heaven” and it is jakōnōr “a tower”.
And they to each other said: We should make a city with a tower whose top is to heaven.