Will I be able get a salary from both a network marketing company as well as the company where I will be working after college using the same PAN Card?

One PAN Card Number is issued to a single person.So your sources for earning won't be any problem.

The main use of the PAN Number is to track your earnings from all sources which allows you to pay taxes on the total amount. You may earn salary, bank interests, dividends from share markets, earnings from 2 jobs earing, royalty, etc. You will need a PAN Number to link them all.