Used when actions or states apply to each member of a group one by one, rather than collectively.
Each problem needs to be examined individually.
Please wrap the parts separately.
Standard kanji spelling; the repetition mark 々 is used for the second 個.
Variant spelling without the repetition mark; less common but still seen.
Compound of 個々 (koko, 'individual, one by one') + adverbial particle に (ni). 個々 is a reduplication of 個 (ko, 'individual, item').