[RPG] Can you break somebody else’s attunement on a magic item

The Shield of Missile Attraction does not automatically attune to characters who use it. Attuning to it causes its "curse" to kick in, but it has no ability to automatically attune or force its wielder to attune. The point you might be missing is that unless you attune to it, you also don't get the resistance to ranged weapon attacks.

Certain magic items require a user to attune to them before their magical properties can be used.

The resistance to ranged weapon attacks is a magical property, and the Shield of Missile Attraction includes the "(requires attunement)" tag, so you don't get the "curse" or the benefit unless you attune.

You may have noticed that I put scare quotes around "curse". Yeah, that's an important point here. The shield grants you resistance to all ranged weapon attacks, so causing them to hit you instead of your allies isn't really a curse - it's the greatest benefit the shield has to offer.

Yes

Many parts of the text on attunement specify that they only apply to items that require attunement. Surprisingly, actually attuning isn't one of those parts. The DMG ( p. 138) states:

Attuning to an item requires a creature to spend a short rest focused on only that item while being in physical contact with it (this can't be the same short rest used to learn the item's properties)..., at the end of the short rest, the creature gains an intuitive understanding of how to activate any magical properties of the item, including any necessary command words.

None of this demands that the item in question requires attunement.

Also note that you must spend a different short rest (ie, another hour) to identify what the properties of this magic item are (attunement does not reveal that). And yet another hour to drop attunement to this item, since you can only be attuned to up to three magic items at a time. Still, you will be able to learn the number of charges an item has without the Identify spell.

NOTE: Spending a short rest to Identify the item (DMG p. 136) will not reveal how many charges the item has left, by rules as written (RAW). Your DM may permit it to do so, but RAW states that the Identify spell reveals charges remaining (both stated on DMG p. 141, and PHB p. 252, in the text of the spell), while the description of mundanely identifying the item (with a short rest) (DMG p. 136) does not.