What does the の add to the sentence?
added to verbs (はしる) for nominalization. It turns to run into a pseudo noun running
Does this work with all verbs?
Why wont it accept most of these "likes" exercises without the ?です at the end?
好き is used as a noun here. If it were an adjective (i-adjective), です/だ wouldn't be required, but since it's a noun, it needs a copula to link it to "走るの".
A lot of the lessons keep putting わたしの in front of brothers and sisters. Of course Duolingo marks it wrong to use わたしの this time...
妹は走っているのが好きです Is not allowed?