。
He can't cope with difficult situations.
Literal
He [topic-は] difficult situation [to-に] cope [nominalizer-こと] [subject-が] cannot-do.
A character-description sentence. 対処する ('to cope with, handle, deal with') takes its target with に, not を — 対処する is one of those verbs where the 'object' (the thing being coped with) is marked as a destination rather than a direct object. ~ことが出来る ('can do X,' 'be able to X') is the periphrastic potential form, using こと to nominalize the verb and 出来る ('can do') as the main verb. Equivalent in meaning to the short-form potential (対処できない), but slightly more explicit and slightly more formal. Common in written analytical prose.