Finding all functions/stored procedures that reference a certain procedure/function?
sys.sql_expression_dependencies
should give you what you want if you don't want to search through the definition of every single object (especially when references may or may not have schema prefixes).
I think you can get what you want with the following query:
SELECT
o.name AS ReferencingObject,
sd.referenced_entity_name AS ReferencedObject
FROM sys.sql_expression_dependencies AS sd
INNER JOIN sys.objects AS o
ON o.object_id = sd.referencing_id
WHERE sd.referenced_entity_name = 'my_object_name';