how can i get data from internal ATS source ?

Assuming you want to use Eikon COM APIs in a custom application for this purpose, use AdxRtList object and set the Source property to the name of your ATS source. Follow this tutorial and change the values in AdxRtList.Source = "IDN"; and AdxRtList.RegisterItems("GBP=", "BID"); calls to use your ATS source name, items names (RICs) and field names.
https://developers.thomsonreuters.com/eikon-com/eikon-desktop-data-api/learning?content=791&type=learning_material_item