Dokuchayevs'k is a provincial town and has no airport. That is why to get to Riga, you need to reach a larger city close to Dokuchayevs'k first, from there you'll be able to fly.
It is impossible to buy direct flights Dokuchayevs'k — Riga, because the former does not have an airport. However, pretty close the following airports are to be found:
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