There's no difference between a 'Discuss' question and a 'Do you agree'/'To what extent do you agree?'
Every essay you write will be
discussing whether or not you
agree. 
If you're having trouble disagreeing, I'd recommend using the word 'Although...' to start you off.
It forces you to consider different points of view: 'Although X, nonetheless, Y'
eg. Prompt: Through his novel, the author suggests that unicorns are wonderful
Contention: Although the author celebrates the beauty and mythical appeal of unicorns, he also reveals their potential for aggressive and spiteful manipulation.
Basically the first part of your contention will be acknowledging the plausibility of the contention, and then the second half furthers it by asserting a statement that's
more true, which will be the focus of your essay.