DailyAsyncApexExecutions Limit from System.OrgLimit can be used to check Async Apex Usage in Salesforce.

Sample Code:

Map < String,System.OrgLimit > limitsMap = OrgLimits.getMap();  
System.OrgLimit objAsyncLimit = limitsMap.get( 
	'DailyAsyncApexExecutions' 
);  
System.debug( 
	'Limit Name: ' + 
	objAsyncLimit.getName() 
);  
System.debug( 
	'Usage Value: ' + 
	objAsyncLimit.getValue() 
);  
System.debug( 
	'Maximum Limit: ' + 
	objAsyncLimit.getLimit() 
);  

Output:

DailyAsyncApexExecutions Limit from System.OrgLimit can be used to monitor the Async Apex Usage in Salesforce. So, use the above code as reference.