How do I see a list of users in my department who are able to override specific documents?

The SEC-001 report in infoAdvantage will provide you with the Security Role that is needed to approve/override.  In addition to running the SEC 001 report in infoAdvantage, you will want to look at the Budget Control Guide that will give you information on the document type and approver/override role that is required to apply an override. 

CORE - Budget Control Overrides Guide Job Aid .pdf