Learn Croatian: Želim probati onaj piling s morskom soli. - I want to try that scrub with sea salt.

The noun sol (salt) is feminine, even though it ends in a consonant. It belongs to the special i-declension group of feminine nouns. In the instrumental case, these nouns end in -i or -ju. Here, we use s morskom soli, though s morskom solju is also perfectly correct.

Why use onaj for that instead of taj?

In Croatian, taj refers to something near the person you are talking to, while onaj refers to something far from both of you. By saying onaj piling, the speaker is likely pointing to a scrub on a distant shelf across the store, or referring to one they both know about but isn't physically present.

Could I use pokušati instead of probati to say try in this sentence?

No, it wouldn't sound natural here. Pokušati means to attempt a difficult action, like trying to open a stuck jar. When you want to try out, sample, or test a product, food, or experience, you should always use probati or the perfective form isprobati.

The word piling comes from the English word peeling. Why is its accusative form onaj piling rather than onog pilinga?