I am looking for an example for simple one table extract and load in same postgres db but separate schemas. source_schema.t1 to target_schema.t2

very doable but most of the time not a use case folks do with Meltano as it tends to make more sense to just write SQL on that Postgres server so using DBT would probably make a lot more sense

okay then is there example available for source is postgres and target is bigquery

https://docs.meltano.com/getting-started/part1 Go with the getting started tutorial here