Assalamu Alaika Ya Shaykh, I have two questions:
1) Will donating plasma nullify fasting (it involves withdrawing of blood, removing the plasma and returning it back to the body)?
2) Can one sell his plasma?
Drawing blood does not nullify fasting except in the Hanbali school (Dr Samer al-Nass). Likewise blood transfusion does not nullify fasting: see https://islamqa.org/hanafi/
As for selling plasma it is permissible in other than the Hanafi school (Dr Samer al-Nass).
Hajj Gibril Haddad