If you're using the Cloud hosted version of Retool, we don't expose this info 
Self-hosted (on-prem) teams can query this info since they have access to the Retool instance's database. As is described in this Retool community post, you may consider adding your on-prem Retool instances backing database as a resource within your organization, then query the users table within your apps as needed.
That said, please kindly note that this solution should be implemented with significant caution in production environments; having the backing database available as a resource may pose issues if not carefully managed (data being inadvertently updated or deleted, the database being over-utilized, etc.). As such, if you choose this solution, here are a few considerations/recommendations:
- Add the database resource using a read-only database user credentials.
- Ensure that your database has the necessary back-up and restore functionality.
- Ensure that the database resource permissions are tightly scoped within your Retool organization.