Check out this video on REST and see if it helps you:
Note: - I assume you are not using GeoAnalytics? - If not - I will move this post to the general Qlik Sense section. GeoAnalytics can on-the-fly geo-code place names, postal codes etc. so under some circumstances there is no need to explicitly retrieve lats and longs.
When applicable please mark the appropriate replies as CORRECT. This will help community members and Qlik Employees know which discussions have already been addressed and have a possible known solution. Please mark threads as HELPFUL if the provided solution is helpful to the problem, but does not necessarily solve the indicated problem. You can mark multiple threads as HELPFUL if you feel additional info is useful to others.