Learn Finnish: Eikö minimalismi ole joskus vaikeaa? - Isn't minimalism sometimes difficult?

You can use the se, mikä structure. To ask 'Isn't minimalism the thing that is sometimes difficult?', you would say Eikö minimalismi ole se, mikä on joskus vaikeaa?. You can also reverse the order for an even stronger focus: Eikö se, mikä on joskus vaikeaa, ole minimalismi?.

Why is the adjective vaikeaa in the partitive case instead of the nominative vaikea?

The subject minimalismi is an abstract, uncountable concept. In Finnish, when you describe an abstract noun or an activity with the verb olla, the describing adjective must be in the partitive case. If the subject were a specific, concrete object, you would use the nominative.

If we wanted to change the focus to ask 'Is it minimalism that isn't sometimes difficult?', could we just attach the question clitic to the noun?

You could attach it directly to the noun (Minimalismiko ei ole joskus vaikeaa?), but it sounds quite clunky. As taught in this lesson, a much more natural way to create this strong focus in Finnish is to use a pseudo-cleft structure: Eikö se ole minimalismi, mikä on joskus vaikeaa? (Isn't it minimalism that is sometimes difficult?).