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.
I think you will be taxed on the profit you made with your eth bag, although I'm not from the United States (US) like you, but have heard of several news about your government imposing a compulsory tax on all crypto returns, so there's a high chance you'll be taxed when you decide to cash out your profit to fiat. slap your self if you are selling eth below 10k, not financial advice 
I'm not sure we are going to see it at $10k soon, so it's better he locked in on the profit he has made already, the market won't be bullish forever just so you know.