Various embroidery designs for stitching and sewing machines can be usually converted between each other with a use of a proper embroidery editor or converter. Both the JEF (Janome) and VP3 (Husqvarna Viking) are fairly common formats so it should give you no trouble converting them using any of the programs listed below.
Open JEF file Open VP3 fileAn embroidery designs manager
A converter for embroidery designes
Advanced version of the popular Embroidermodder
A free embroidery editor and converter
An embroidery editor and converter