Before starting, you have to make sure, your SLA synchronised with Custom fields.
Please check the Documentation here - SLA in Jira Custom Fields
If data successfully synchronised, and you can see the SLA Status and Target date in issue layout, start from 2nd item
Then, using the name of SLA Configuration Goal, type it in the JQL fields to create the Filter.
So, by the following request you will get the list of issues that are under the particular SLA and its Goal.
"SLA status for Time to Resolution" != EMPTY
In this particular case field name = “SLA status for Time to Resolution”, and it’s getting SLA status once any changes in the issues. So, it’s always relevant and synchronised.
See, also - How to prepare the SLA Time and Report Gadget using native Jira Gadgets