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Not exactly out in the open, but relatively easy to obtain early on: There is a hidden wall in the sewers beneath the gang compound across the street. Being able to punch through walls makes it easier to locate, not the vision enhancement.
Make sure you purchase two Praxis kits from every LIMB clinic. Make sure you always hack every locked object in sight (the shear amount of exp you get practically nets you 5 free levels/points). And in order to find most of the hidden Praxis kits you NEED the ability to:
Smash through thin walls Jump 9m Fall from any height Hacking
I can't remember if 'Immunity to EMP/Electricity' and 'Gas Immunity' helped me find Praxis points but they did gain me access to secret locations.
At the end of my first game I had EVERYTHING I wanted and I was only 15 points short of purchasing everything. I didn't use a guide to find every Praxis point either. I didn't touch the Stealth section (7 points), Typhoon (2 points), Multi Takedown (2 points), and some Hacking and Vision augs were useless.