I imagine there will be a ton of places during the game where you can earn this, but I will tell you how I earnt this right at the very start of the game! Some ppl like to get a Cheevo done early, so for those guys, here's how;
At the very start, playing as 2099 Spiderman, you trail Walton around in the vents. This is both the credits section, as well as a tutorial. When you enter the room where your first encounter of Spiderman 2099 combat begins, you are in the right place.
Some robot guards appear on your left, being wailing on them with X & Y. This starts your combo meter - once you defeat them the combo meter is held briefly, long enough for more to appear and for you to continue your assault.
Around this point you learn the 'long range grab' move [RB]. Do this, and when you have the enemy in range hit X and you will perform a flurry of quick blows - THIS is how you build your combo meter as Spiderman 2099. Rinse and repeat until it pops!
I think I had a meter of around 59 when the last enemy dropped.
I did it on the starting level of difficulty, which I assume to be 'Normal'.
Hope this helps!