A common cause of slow SQL Server performance is a heavy database application workload—the nature and quantity of the queries themselves. Thus, to analyze the cause of a system bottleneck, it is important to examine the database application workload and identify the SQL queries causing the most stress on system resources. To do this, you can use Extended Events and other Management Studio tools.
The basics of Extended Events
How to analyze SQL Server workload and identify costly SQL queries using Extended Events ...