Which activity is used for detecting duplicate message processing

CheckPoint activity - Specify the uniqueID for the duplicate key field and engine maintains list of these key fields. When a process come to checkpoint activity with the same value for duplicate key which already exists, it throws a DuplicateException. An error transition can then handle this case

 

The Checkpoint activity performs a checkpoint in a running process
instance. A checkpoint saves the current process data and state so that it
can be recovered at a later time in the event of a failure. If a process
engine fails, all process instances can be recovered and resume
execution at the location of their last checkpoint in the process definition. If a
process instance fails due to an unhandled exception or manual termination, it
can optionally be recovered at a later time, if the process engine is configured to
save checkpoint data for failed processes. See TIBCO BusinessWorks Administration
for more information about recovering failed process instances.
Only the most recent state is saved by a checkpoint. If you have multiple
checkpoints in a process, only the state from the last checkpoint is available for
recovering the process.