If you are a Trader (buying to sell for profit), Zakat is due on the full market value. If you are an Investor (long-term), Zakat is only due on the company's liquid assets. Scholars often use a 25% proxy of the share value as a safe estimate.
Is Cryptocurrency Zakatable?
Yes. Crypto assets like Bitcoin or Ethereum are treated as digital cash. Regardless of intention, most modern scholars suggest calculating Zakat on 100% of the market value once the Nisab is met.