I don't know Superboy that well, but I do somewhat know Martian Manhunter and I've been trying to find the issue this is from for months upon months [click here for the pic] now with zero luck. Any ideas?
Obviously, it's not from DC Encyclopedia, and several others can also be ruled out. The costumes, art and layout suggest it's from (or concurrent with) JLA (Volume 1) or the later part of Young Justice (Volume 1). Check the summaries; if they don't help, you can look for the comics at Comixology.