1, Can we create an external triggers to schedule Qlik Replicate task.
Externally you can do whatever you like. You can use the Enterprise Manager 'RunTask" API or the REPCTL EXECUTE command to run a task. So that's not to schedule, but run there and then. To Schedule I suppose you could generate some JSON and Import that, but that get's clumsy due to the 'merge' strategy with import.
2. Can we send email or alert if any table structure changes at source side.
No, not really. You'd have to scan logs, compare SQLlite databases, or use REPCTL dumpmetadata
3. Can full load data will be stored in audit table, i.e. in _ct table.
No. Not with Replicate in a normal task. There is nothing to stop you from creating your own transformations adding header__ columns filled with appropriate date targeting a target table renamed to __ct and flull-load into that but it would be a second task, and thus possibly out of sync.
