I have 2 questions, how do you know which way the current is going and second what is the best way to troll the current, with the current - against the current - or across the current
Lake Michigan currents
Current predominantly goes around lake clock wise in winter and counter clock wise in summer, so North to South in Milwaukee. Fish face the current naturally, so trolling into it is better.
There are many exceptions to this and reason people invest in probes like depth raiders or fish hawk. It is very common to have to troll 1+mph faster in one direction vs other to compensate.