At least in the English version, when you start to enchant something, the window opens with the weapon list, and you have to switch to the armour or jewelry lists if you want to enchant one of them (using the shoulder buttons in the Xbox version; don't know about PC, probably the same as switching inventory categories).
In the equipment list, it should show the fraction of used to total enchantment slots on the right; if they are all greyed out, then there would either be nothing, for no enchantment slots, or (1/1), (2/2) or, very rarely, (3/3).
Once you select a piece of equipment with an open enchantment slot, going through the list of available enchantments, any missing ingredients should be shown on the left in red (the text is green if you have enough), and a statement shown in red if the equipment already has the selected type of enchantment (you can not add more than one of the same type).
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