Why the 747 testing GE-9X doesnt have a winglet?
That's because its been removed for testing. The aircraft used in for flight testing the GE-9X belongs to GE and is a modified JAL 747-400. 


  The aircraft, a former Japan Airlines -400, was acquired by GE in 2010 and 
  following maintenance and interior modification in Xiamen, China, 
  by Taikoo Aircraft Engineering, was delivered to Evergreen Aviation 
  Technologies in Taiwan for installation of data racks and instrumentation. 


For carrying out the testing, GE has carried out a number of modifications for maintenance and testing:


  ... modifications are also planned to reduce the chances of aero 
  elastic interaction between the extended wing of the 747-400 and the 
  GE9X mounted on the inboard left strut. GE has already removed 
  the standard winglets because these add unnecessary weight and a 
  maintenance burden to the aircraft’s flight-test role. Later this year, 
  the outer 6 feet of each wingtip also will be removed, ... Designers say the stiffer wing will reduce potential exposure to limit cycle oscillation and maintain an unrestricted test envelope.


Quotes from archive.org. Original ariticle appears to be from aviationweek.