This does what you need and if this helps, try to use SQL paramters instead of constructing the SQL statement to avoid SQL injection
Event_id like '"+ddlEvents.selectedValue+",%'
or Event_id like '%,"+ddlEvents.selectedValue+",%'
or Event_id like '%,"+ddlEvents.selectedValue+"'"
Your questin heading says senicolon (;) seperated and the example you have provided says comma (,) and the solution is based on comma seperatation and you may have to slightly change the query if it is semicon
Just noticed AmolPandurangBorkar875 has provided the similar solution already, I was late