The simplest method is the local monitoring console. Click Settings > Monitoring Console. In the app bar, click Search > Scheduler Activity: Instance. In the Historical Charts section of the dashboard, you can see various panels related to search scheduling.
If you find many deferred searches, you have three options:
1. Optimize scheduled searches.
2. Adjust limits. See https://docs.splunk.com/Documentation/Splunk/latest/Admin/Limitsconf#Concurrency.
3. Add CPUs. (This is often Splunk's recommendation, but try optimization first.)