I am a Spanish resident (not a Spanish citizen yet) that would like to work for the summer up to 6 months in the Netherlands. Can I do it and what it will be the procedure?
The details depend a bit on your citizenship, the nature of the work and possibly your status in Spain but basically you need a work permit/visa as you would if you would be coming directly from outside the European Union (usually something called a Gecombineerde vergunning voor verblijf en arbeid). For less than three months, you might also be able to stay in the Netherlands without a visa but you would still need a work authorisation (in Dutch: tewerkstellingsvergunning).
Unfortunately, your being a Spanish resident does not generally entail any right to work in the Netherlands or access to any special procedure to do so, beyond what's already available based on your citizenship and your personal situation.