If you lost your charger for your Nook, you have some options for Nook charger replacement. What you need depends on what kind of Nook you have.
The Nook Color and Nook tablets used a special adapter and cable to help it charge faster. In a pinch, you can use a regular Android-compatible charger with a standard micro USB connector. The original charger worked faster, so getting an original one off Ebay is a better long term solution. While you wait for that to arrive, use a standard charger for any Android phone or tablet.
Nook e-readers with old-school e-ink screens use a regular Android-compatible charger. Any charger for a garden-variety Android phone or tablet will work for charging a Nook Simple Touch or other Nook e-readers.
Last and least, use a micro USB charger cable to plug your Nook into a computer. It won’t charge as quickly, but it will work if you can’t find a wall charger.
If you’d like some more generic advice about AC adapters, here are my recommendations for general AC adapter substitution.