Its LOTS of practice,
There are two ways you can approach this, one is more aimple but in my opinion not the best for a dagger, the other is relatively more complex but mentains the integrity of the tip
1, treat the dagger as if its a simple knive, and the double (second) edge as a swedge, however this removes lots of material from the point which weakens it
2 (i am combining this advice from information I got from Bill Harsey and Nathan the machinest) make a line in the middle of the blade along its length. Grind till you reach the line
When you approach the point you will need to 'twist' the blade (grind less area)so you would leave meat at the point for strength