KRC2 or KRC4?
Installing a WiFi device directly on the robot is a questionable proposition. However, if the robots are connected to a WiFi access point via Ethernet cable, then it is entirely possible to connect the laptop via WiFi.
I've never been able to make file transfer through VNC work, but I must admit I never tried very hard. Generally, I create a special isolated directory on the D drive of each robot with full read/write network access, and use that as a remote network drive to transfer files. Then I use the KUKA HMI via the pendant or the VNC to transfer the files from the isolated transfer directory to the /R1 RAM drive.