We simplified keeping track of your shared custom picklist values. Each global picklist’s detail page shows where its picklist value set is used. This feature is available in Salesforce Classic only.
When you create a global picklist, the list of values you specify becomes its picklist value set. When you create custom picklist fields and base them on the global picklist, they inherit that picklist value set.
To see which picklist fields use a particular picklist value set, go to the Picklists node in Setup. Select the global picklist that has the value set you’re interested in. The picklist fields that share the picklist value set appear under Fields Where Used.
View Which Fields Use a Picklist Value Set