Learn Croatian: Moramo razumjeti traumu za pravo iscjeljenje. - We must understand the trauma for true healing.

No, because it would completely change the meaning. The preposition za + Accusative is used here to express a purpose or end goal (in order to achieve true healing). If you used kroz pravo iscjeljenje, it would mean 'through' or 'by means of' true healing, implying that healing is the method we use to understand the trauma, rather than the goal we are trying to reach.

What case is pravo iscjeljenje in, and why does it look like the Nominative?

It is in the Accusative case, which is required by the preposition za when expressing a goal or purpose. Because iscjeljenje (healing) is a neuter noun, its Accusative form is identical to its Nominative dictionary form. The adjective pravo (true/genuine) simply agrees with this neuter Accusative form.

I know razumjeti means 'to understand', but is it perfective or imperfective here?

Razumjeti is actually one of the few bi-aspectual verbs in Croatian, meaning it can function as either perfective or imperfective depending on the context. Here, it functions imperfectively to describe an ongoing state (we must maintain an understanding of the trauma). For a purely perfective action ('to grasp' or 'to realize' a concept suddenly), Croatians often use the verb shvatiti.

I've seen the word pravo used to mean 'straight' or 'law'. How do we know it means 'true' here?