Hi Sudheer,
Please find below response for your queries.
1. SQLLDR Load depends on the TNS entry . Kindly check the TNS Entry first ( use TNS ping to verify). Check the "Instance/dblink (Data Server) in the Target Data Server in the Topology(which you are using as Staging) .
2. If you are accessing the sequence in a variable , write your query like "select ..Nextval from dual". Check the logical schema, if its pointing to the correct physical schema with your execution context.
Similarly , if you are accessing the sequence in an Interface use only ..Nextval
3. While migrating your code from Dev to Any other Target Repository , kindly use smart export to export your code. This will move your Scenario/Project along with the required connections in the Topology .if you are adding some new connections to your existing code, Kindly smart export the changed code (with a new scenario version preferably) , this will move the new connections.
Let us know if you are looking for this else please elaborate your question.