1. Should you read the whole passage before looking at the questions?
2. Should you go to the questions first, then skim/scan to find the answers?
My answer to question 1 is no. You don't have time to read the whole passage unless your English is almost 'native speaker' level.
My answer to question 2 is yes and no.
Yes - go to the questions first.
No - don't skim or scan unless the question contains a name or number.
My advice is to do the questions one by one. Instead of skimming or scanning, read the passage carefully. The answers to most question sections will be in order in the passage, so you will gradually read the whole passage as you find the answers.