Learn Finnish: Tämä rikkomus tapahtui ilman asiakkaan suostumusta. - This violation happened without the customer's consent.

It attaches to the stem of the verb rikkoa (to break). The -mus suffix forms a noun that represents the result of the action. So, an act of breaking becomes a 'violation' or 'infraction'.

Is suostumusta also formed with the -mus suffix, and what is its root verb?

Yes, its base form is suostumus, derived from the verb suostua (to agree or consent). The suffix turns the action of agreeing into the abstract noun 'consent'.

Why is the word suostumusta in the partitive case here?

It is required by the preposition ilman (without). The word ilman forces the main noun of the phrase it refers to into the partitive case, which is why we see suostumusta instead of the nominative suostumus.

If ilman forces the partitive case, why is asiakkaan (customer's) in the genitive case?

Because asiakkaan is acting as a possessive modifier for suostumusta (the customer's consent). Possessive modifiers stay in the genitive case to show ownership, even when the main noun they modify is forced into another case by a preposition.