This is always one of the tricky ones. Often it is hit or miss. You might try coming back here with another double jump character -- Sometimes different characters move a little differently. I remember the times I did make it I was almost directly under the grate and then I sort of jumped up and slightly towards the grate. Very frustrating the way they set it up.
I recommend trying other double jump characters since they often have slightly different patterns. Somedays I cannot get it no matter how hard I try and other times it happens the first time. I am not sure if it is me or something I am triggering within the game. I might get it after a 100 tries.
Caution: Once you get in, there are a few death traps to watch out for (You will need R2 for the main one). The most frustrating thing is to finally jump in the grate and accidently jump right back out (I think I lost hair from that idiot move).
