I think altcoins pump and dump are highly seen in newer projects as the team can once in awhile show they are still around, some will only pump once and that's it while in major projects, their developments spikes the pump and the dump is not as bad as those of the newer projects, which is also mostly as a result of market reactions. Now about knowing if a coin will pump and dump, it is always hard to tell because no one can correctly predict anything in the crypto space, hence whatever coin or mostly new coins you are investing in, with the hope of pump, you might only end up risking your money. Lastly, my humble opinion is, check out major coins like Ethereum, ADA and so on.