。
I have to prepare for the English exam.
Literal
I [topic-は] English [possessive-の] exam [possessive-の] preparation [object-を] must-do-[なければいけない].
~しなければいけない ('must do') — one of three nearly synonymous obligation forms. Uses the double negative: ~なければ ('if not') + いけない ('it won't do'). 準備をする ('to prepare') takes の chains for nested possession: 英語の試験の準備.