SQL Server 2014 View any Live execution plan in Activity Monitor
You have to enable trace flag 7412

DBCC TRACEON (7412, -1)




According to blog post, you have to enable xEvent: query_post_execution_showplan

Warning, despite that this feature works starting SQL Server 2014 SP2, it can introduce significant overhead - up to 75%.:



Starting SQL Server 2016 SP1, this was changed and the overhead is only 1-2%
(in case of trace flag 7412) or 15% if query_post_execution_showplan xEvent enabled

In 2019 it is enabled by default

Details:

https://blogs.msdn.microsoft.com/sql_server_team/query-progress-anytime-anywhere/

Permissions:


  Requires the database level SHOWPLAN permission to populate the Live
  Query Statistics results page, the server level VIEW SERVER STATE
  permission to see the live statistics, and requires any permissions
  necessary to execute the query.