And now for the less honourable route. How many Praxis points that you can earn in a single playthrough is indefinite, if you are willing to ply an exploit.
Gameplay on OnLive, where the grind was done, cannot be hacked nor modded. In the Brag Clip, what is seen is the fruit of hours of accumulating the +500 XP bonus from hacking Adam Jensen's computer + 10 nuke viruses and 10 "stop! worms" rewards from other hackables as a cherry on top. I culminated by loading a save earlier in the game and finally accepting the rewards upon hacking the first possible hackable PC to play through as much of the game as possible at practically maxed praxis (I never bought the extra energy cells).
Here are instructions that I wrote a while ago. While quirky, it stills contains key, scientific data that...other, less comprehensive, yet overly common tutorials lack.
"In the video-game "Deus Ex: Human Revolution" (#DXHR, #DX:HR), there is an exploit/glitch to get lots of hack rewards. By most, it is called "the infinite XP/praxis glitch", but I coin it the "hack reward accumulation glitch" or "#HRAG" for short. Originally, I called it the "hack bonus accumulation glitch" (#HBAG) but changed the name because the game uses the term "reward(s)". In the shortest amount of words, how-to: quick load at reward(s) pop-up. Wordier: Although inexplicit (the OnLive version of the game never tells you), the "F5" and "F8" function keys act as quick-load and quick-save, respectively. It is by means of quick-loading at the menu, that is a pop-up after successfully hacking which displays hack rewards, that at the next successful hack, the hack reward(s) earned from the previous successful hack (quick-loaded from), will be added on. This can be done continuously and across saves, so that (for example as my case) enough XP can be stacked to earn as much praxis as desired to get every ability at the first hackable PC in the game (why PC instead of keypad is explained later). The data of stacked rewards is only stored while the game is active; quitting the game resets all progress. Adam Jensen's PC is the most efficient to earn XP (500), but still takes hours to earn enough to get all abilities. Keypads can stack rewards, but not from one keypad to the next. Stacking, hacking from a PC to a keypad, then back to a PC is OK, but hacking from a PC to a keypad to a keypad will erase all progress. The accumulated rewards don't appear on a keypad's rewards pop-up, but are still stored in the memory buffer. If a PC is hacked after the keypad, the bonuses reappear. I don't remember if stacked rewards can still be obtained by truly completing (confirming the rewards pop-up) a keypad hack, but I assume no or else I would've stacked to the true first hackable (which is a keypad)."
Note: Augmented edition, but it shouldn't matter.