How to identify database is primary or replicated? is there any procedure?

This is simplest observation for Primary database.

Primary database always has rep agent running.

You can check , rep agent is configured for adatabase or not, by executing sp_config_rep_agent.

You can check rep agent is running for configured database as

sp_help_rep_agent "dbname","process"
go

If its reporting spid , it means rep agent is running and this database will be replicating the tables.

In two way replication, your primary and replicate both databases will be running rep agent and wrt each other you can decide primary and replicate database.

If you still have any query, please let me know. Thanks.