You can learn about Replication (Streaming/Logical) and WAL and then you can easily find many case examples online, there is no scarcity of information on Postgres.
I am learning postgres. If I want to resolve any critical activites at high level, I want to learn WAL and replication methods.
Could u all help me with questions or problems or exercises such that If I solve those problems, I will be fully trained to take care of high level problems.
Read the official documentation and it's more than enough for you to learn these.