In addition to listing items and completing offers, another way to get XNK into your Listia balance is to deposit it into Listia, described here. To do this though, you'd first need XNK stored outside of Listia.
The primary way of getting XNK is to buy it on exchanges that sell XNK. Currently, one such exchange is IDEX. To use this service, you will need a basic understanding of Ethereum wallets, ERC20 tokens, and cryptocurrency exchanges.
We will be adding more information about this process soon, so please stay tuned!