If I invested 30k in Ethereum and when my investment goes up to 60k, and I sell 30k just to get my initial investment back, will I be taxed on that? I live in the United States and just bought Ethereum this year.
Taxation differs from country to country. So you will have to do a little research and find out the taxation guidelines for cryptocurrency for your country.
Also, you don't have to pay the tax just for selling the cryptocurrency. You will only be taxed when you withdraw the gains to your bank account.
You can keep buying and selling until you want. Taxations levy only when you withdraw the profits for fiat.