Taxes for citizen of EU country #1 living in EU country #2 and working from home for non-EU country #3?
You will almost certainly be paying taxes in Czech Republic, short of being American of Eritrean, citizenship has little to no bearing on tax. If you are working from home, you will probably be a contractor. In Romania you would work through either an SRL or you would set up a PFA. Essentially a limited company or a sole trader. You will need to find the Czech equivalents. I would advise finding a small business accountant. They will be able to advise what is the most cost effective solution, in some countries (like my one) you can save considerable amounts of tax by working through a company. There is a link with some information.