Checking technical information associated with screen field in SAP without any documentation

When you have report selection screen option, you can use Ctrl+S to enter the variant screen. Press Technical Name button to display technical name information for the respective field.

In case you want more information related to parameter field, you can write an ABAP code to see the definition.
Mostly, F1 key is used to get all the details about the technical details of a particular field as shown in below:

Also if you want to see Technical name of objects in SAP ECC Easy access for all the modules, you can navigate to Extras -> Settings