Learn French: Ce qu'il a fait est impardonnable : il a poignardé mon ami. - What he did is unforgivable: he stabbed my friend.

This lesson is about the indignant independent subjunctive, but there isn't a subjunctive in this sentence. How could I express this using the lesson's grammar?

You could drop the introductory clauses and use an independent past subjunctive to express your shock directly: Qu'il ait fait ça ! (That he would do that!) or Qu'il ait poignardé mon ami ! (That he would stab my friend!). The structure Que + [subjunctive] ! shows strong emotion or indignation without needing a main clause like 'Je suis choqué que...'.

Why do we use ce qu' here instead of quoi for 'what'?

When 'what' means 'the thing that' at the start of a clause, French uses a demonstrative pronoun (ce) plus a relative pronoun (que or qui). Here, the verb a fait needs a direct object (he did the thing), so we use que. Because il starts with a vowel, ce que il contracts to ce qu'il.

Is the verb poignarder related to the word for 'fist'?

Yes! It comes from un poignard (a dagger), which traces back to le poing (the fist). To stab someone in French is literally to 'dagger' them, using a weapon held tightly in the fist.

I notice there is a space before the colon. Is that a typo?