This costume, worn by Eric Menyuk during his second appearance as the Traveler in Star Trek: The Next Generation, is from the 4th season episode 'Remember Me'.
In this episode Wesley Crusher, while experimenting with some warp equations from the first visit of the Traveler, accidentally creates a shrinking pocket universe and traps his mother. The Traveler senses what has happened and appears, in this costume, to help Wesley save the day.
A screencap from the episode is included.
