(1) Launch sketchDump
(2) paste Sketchfab link 
(3) after it says "Decryption Complete" , there will be a "downloads" folder created in the same folder you launched the app from. 
(4) Open the "downloads" folder then the folder for whatever you downloaded. 
(5) get the entire directory link to the file.osgjs file. you could do it through Home > Copy Path . Copy and paste that link into the app again. 
(6) A .gltf has been created, in the same folder of whatever you downloaded. You can open this .gltf file in blender. 

Additional note: You cannot open the .osgjs file in Blender because Sketchfab has a 2-step encryption. When you initially decrypted, it was to make the .osgjs file. But you need to decrypt it through the app again to get the real file.