You can just create those variables in your PrintLabel.js .
You just use the field ID like Chris is mentioned. If in edit mode you can open up console(F12) and type _fid_3.value and it should return the value for that field on the form. 3 usually is Record ID I think but you get the idea.
In console you can type gDBID from a table and get the DBID. You just need the formula text field to load the PrintLabel.js then just create another formula text thats an html button and wrap the print label function on the click like this
$("#qbu_yourBtn").on("click", printLabel())
Good luck!
-Chuck@Chuck.Support