A common mispelling of Fuck, caused by the fact that the letter J is next to K on a typical QWERTY keyboard, And that the user may not be quite a good a typist as they thought they were.
It may also be possible that the user is illiterate.
what a stupid Fucjer
The use of one's feet to "Pat" something down.
"hey you bastard, don't tramp on my flowers!"
"If you tramp the soil down well, they'll never find the body"