How to get the parameter values of a stored procedure that's in the middle of execution?
For SQL Server 2016 you need to have the query profiling infrastructure enabled in advance with trace flag 7412 or an extended events session capturing query_thread_profile (and be on at least  SQL Server 2016 SP1) but then can use

WITH XMLNAMESPACES
   (DEFAULT 'http://schemas.microsoft.com/sqlserver/2004/07/showplan')
select query_plan.query('//ParameterList')
from sys.dm_exec_query_statistics_xml(@session_id)


and see the ParameterRuntimeValue and ParameterCompiledValue from the execution plan of the statement being executed. 

For SQL Server 2019+ the infrastructure is enabled by default so the above will just work. 

This might not be all the parameters of the stored proc however as it will only include params used by the execution plan.