Learn French: Tu sais ce dont elle souffre ? - Do you know what she suffers from?

The verb souffrir requires the preposition de when saying you suffer from something (souffrir de quelque chose). Whenever a verb takes de, its corresponding relative pronoun is dont. Because we are saying 'the thing that' she suffers from, we combine ce (the thing) and dont (from which) to make ce dont.

In English, we put 'from' at the end of the sentence ('what she suffers from'). Why isn't there a de at the end of the French sentence?

In French, you can never end a sentence with a preposition. The preposition de is already built into the word dont. Therefore, ce dont covers both the 'what' and the 'from' in your English translation.

Could I say Tu sais de quoi elle souffre ? instead?

Yes, absolutely! Tu sais de quoi elle souffre ? is another very common and natural way to ask 'Do you know what she suffers from?' in everyday spoken French. Ce dont is simply another way to express the exact same idea, and it is great to understand both.

Why does souffre end in an 'e' if the infinitive is souffrir?