How do people calculate what could be the price depending on market cap?
For example, people saying that DGB will hit 1$ at 8billion market cap
There are no ways to calculate the altcoins future price depending on marketcap, the marketcap can change every time and it is one of data to makes analisys fundamental of digital coins, but doesn't mean it will be work 100%, if you want trading altcoins will be good start learn about analisys technical to makes prediction of price.