It greatly depends on the legal definition of the digital currency in the country in question(Crypto recognition and legality in different countries), as well as the tax system utilized in the particular country. Some countries use a wealth tax instead of CGT, others use both or income tax, and yet others use either income tax or Capital Gains Tax (CGT), but no wealth tax.
Disclaimer: This is not a legal, tax, accounting or investment advice. It is general information which should only be used for introduction purposes. You should consult with a tax/legal specialist.