Use Shift+Page-up and Shift+Page-down.
Look under Options->Terminal of your kvt window.
When I do a ls, first I select with the mouse the desired text, press CTRL+C, then I make the other app active, point the mouse to the relevant part and press CTRL+V. Alternatively, highlight the text by dragging with the left mouse button down and paste by clicking with the middle button (or both buttons if you have 3 button emulation set and you are using a two button mouse).
Try: kvt -sl <number>
By the way, if you execute kvt with some unknown option eg. kvt -x, kvt will print out a list of valid options.