http://answers.yahoo.com/question/index?qid=20100410212819AA54q7u
http://mycheats.1up.com/view/section/3172942/28732/pokemon_heart_gold_soul_silver/nintendo_ds
http://www.psypokes.com/hgss/tmhm.php
These kind of things are easy to look up, here are locations, but it's not hard to google.
It's in the Goldenrod Tunnel's warehouse, next to the Radio Director. This is the only Sleep Talk TM in the game.
TM082 (Bulbapedia)
