The back faces of some cards with craft refer to cards "used to craft" it. This refers to the cards exiled as part of the cost of the craft ability of the front face. Those cards are considered to be "used to craft" that permanent as long as they remain exiled and the permanent remains on the battlefield, even if the permanent's controller changes or some of its characteristics change (because of a copy effect, for example.)

Craft abilities are activated abilities. You can spend mana from The Enigma Jewel's activated ability to activate its own craft ability, for example.

If a card that isn't a transforming double-faced card becomes a copy of a card with craft, it'll stay in exile if you activate the craft ability. It won't return to the battlefield.

Any choices made when the ability resolves won't have been made yet when it's copied. Any such choices will be made separately when the copy resolves.

If the ability has damage divided as it was put onto the stack, the division can't be changed, although the targets receiving that damage still can. The same is true of abilities that distribute counters.

If the ability that's copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode or modes. You can't choose different ones.

If an activated ability of an exiled card used to craft Locus of Enlightenment references the card it's printed on by name, treat Locus of Enlightenment's version of that ability as though it referenced Locus of Enlightenment instead.

Locus of Enlightenment has only the activated abilities of the exiled cards used to craft it. It doesn't gain keyword abilities (unless those keyword abilities are activated), triggered abilities, or static abilities.

An activated mana ability is one that produces mana as it resolves, not one that costs mana to activate.

The copy is created on the stack, so it's not "activated." Abilities that trigger when a player activates an ability (such as Locus of Enlightenment's own triggered ability) won't trigger.

The "only once each turn" restriction applies to each ability individually, even if multiples of the same card were exiled to craft Locus of Enlightenment. For example, if two of the same card were exiled to craft Locus of Enlightenment, it will have two instances of each of that card's activated abilities. Each of those abilities may be activated once each turn.

If the ability that's copied has an X whose value was determined as it was cast, the copy has the same value of X.

The copy of the activated ability created by Locus of Enlightenment's triggered ability resolves before the original ability.

The copy will have the same targets as the ability it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them.

If the materials required include multiple objects, you may exile some of them from among permanents you control and the rest from among cards in your graveyard. You don't have to choose all permanents or all cards from your graveyard.

You may exile tokens you control as part of the materials required. However, because they aren't cards and won't stay in exile, any abilities that refer to what you "used to craft" the back faces won't refer to anything.

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have colons in their reminder text.