If you have exact cashier id to check with then, follow any below step:
1. Split the field into parts and then create a field with sub string of that. Now put the field in filter shelf and drop count of order in text field to show count of these orders.
2. Use contains() field to check if order id contain cashier id, and then form a group. Now perform count aggregation on the field to get the count of orders.
Hope this helps you.