难道 (rhetorical: don't tell me …?)

"Surely you don't mean…?"

• don't tell me ...难道nán dào turns a statement into a rhetorical question of disbelief.
• don't tell me ...难道nán dàoyou你nǐto forget忘wàng(completed / change)了le？ = "don't tell me you forgot?!"
• It expects the answer "no, of course not".

don't tell me ...难道nán dào … ？

• don't tell me ...难道nán dào opens a rhetorical question, often closing with (yes/no ?)吗ma.

don't tell me难道nán dàoyou你nǐforget忘wàng了le吗ma？

• don't tell me ...难道nán dàoyou你nǐto forget忘wàng(completed / change)了le(yes/no ?)吗ma？ = "don't tell me you forgot?!"

Not a real question

• You're not really asking — you're expressing surprise or doubt.

Recap

Read the full reference: HSK 4 grammar — Adverbs.