If I buy a bitcoin a bitcoin for 10000 dollars, and sell for 10200
Obviously I have gained 200 Usd.
But then out of the gain I must pay commision, if this has happened what exchange would have been least commision?
It depends on what exchange you are going to use but so far Binance is the lowest in terms of fees and specially if you use BNB token to pay for the fees that will be 50% off from the regular fees that pay. Bittrex offers 0.25% fees on every trade and that is a flat fee compared to Binance which is only 0.1%.