how to migrate geometry field from postgresql(PostGIS) to sdo geometry field oracle
Welcome to SO.
I'm not an Oracle expert, but I believe you could export the PostGIS geometries as WKT (Well Known Text) and then in Oracle convert them from WKT to SDO Geometry
In PostGIS you can get a WKT representation of your geometry using ST_AsText
Further reading: convert Postgres geometry format to WKT