。
I have to prepare for the English exam.
Literal
I [topic-は] English [possessive-の] exam [possessive-の] preparation [object-を] must-do-[なくてはいけない].
~しなくてはいけない combines ~なくては + いけない. Japanese obligation expressions follow the pattern (negative conditional: なければ/なくては) × (predicate: ならない/いけない), giving four functionally equivalent variants. Casual speech contracts these to ~なきゃ / ~なくちゃ.