Is it permissible for a Muslim accountant to receive a portion of an interest-based prize due to his involvement with it, and is writing checks for interest-based banks in daily transactions permissible (halal)?

Most competitions organized by usurious banks are impermissible (haram). It is not permissible to accept a prize from them unless you are poor and in need, in which case you may take only what suffices your need and spend any surplus on charitable causes, while outwardly expressing your disapproval. Writing checks that involve usury is not permissible, as it falls under cooperation in sin. The Prophet (ﷺ) cursed the one who consumes usury, the one who feeds it, the one who writes it, and its two witnesses.