It's easiest to do this in NHL Threes Now, which is you vs the CPU offline. Play as an NHL All Star team, and play against a weak team like Team Japan. I also set the difficulty to Rookie.
Make sure you click
in the team selection screen, to lock position as a winger or centre.
Now to do a manual one timer, when you don't have the puck, you need to hold down
, and pull back on the right stick, when the CPU passes the puck to you, you need to push the right stick forward. The timing can be a bit tricky to get down, I found you need to anticipate the pass a bit and push forward before the puck gets to you.
Hope this helps!