The Slack integration in Jira does not display how many and which users currently have personal notifications configured with their Jira account. This could be important to figure the owner of the subscription.

Workaround

You can get the related users using a SQL query along the lines of:

select cwd_user.lower_user_name, cwd_user.lower_display_name, cwd_user.lower_email_address from propertyentry, app_user, cwd_user  where property_key like '%slack%' and propertyentry.entity_id = app_user.id and app_user.id = cwd_user.id;

Keep in mind that the 

'%slack%'

portion results in a really broad search and that you should narrow this to exactly the property that represents the connections / users you want.