The specifics of test taking really shouldn't matter too much. You will be taking a test, it will last 1 hr, and you'll have pen and paper. In any case, to answer your questions:
a) This entirely depends. If you are the only person applying, you will obviously be taking the test by yourself. However, if you are applying as part of a milkround/fall recruiting, you may be taking the test in a large room with lots of other applicants. Additionally, the test could also be done on campus for campus recruiting.
b) Usually there will be a clock in the room. You can also bring a watch (not a smart watch). As for whether someone will be checking in on you, probably but you won't necessarily have someone in the room with you the whole time. If you are thinking whether you can cheat, don't.
c) PST is in English, and I haven't heard of it being translated into a different language. However, for some offices where level of English is generally very low (e.g. Japan), this might be the case.
To Prep, you should start with practicing with the official tests on the McKinsey Website (they have 3). Additionally there are a number of (free and paid) practice tests online. PrepLounge is also offerring a new set of practice materials which might be worth investing in. I would also recommend:
- Practicing speed reading
- Practice quick mental maths
- Practice being comfortable with estimating/rounding - a lot of questions in PST test your ability to calculate things in an order of magnitude / rounded way, as it would take far too long to do all calculations in a precise way
- For the verbal questions of the exam, I would recommend practicing with GMAT critical reasoning and reading comprehension questions (many resources for this online + you can buy GMAT practice books)