Hi, I'm an egineer, working full time, but I'd like to get a better job, in fields I have no experience in.
Quite a lot of job offers that I'm interested in require a master degree in specific fields or even PhD. I don't want to stop working, I thus went to look for info and programmes and now I'm completely lost in how all this works. I just would like to get trained and learn new things while still being able to get a salary out of it. Is that possible by doing a thesis? What other option is there? To who I should seek informatio from?

I am doing an engineering PhD and I can tell you an engineering PhD does not improve your job prospects but severely curtails them. Employers will suddenly think you are overqualified for most jobs and the jobs you are qualified for are very competitive. A masters is a far better investment and better for your overall job prospects. Most reputable universities offer part time masters via distance learning over 2-3 years, which require 2-8 hours a week of work (I am guessing). Masters allows a certain degree in specialisation in a specific sub field (bioengineering, business, H&S etc) and you can choose the course that suits your interest the best. Most of the work will be coursework or exam based. I would only recommend a PhD if you are passionate about your project/topic as it is a far more substantial degree than a masters (with regards to effort).

How do you know you get seen as overqualified if you're still doing your PhD now?
I don't kknow how to say it but getting back to regular studying is pretty much my last resort if I even consider it: I'm a bad student, I can't work if it's not for a real reason, a real project, it's beyond me. As far as passionate goes (and that's one of my main problems), I actually like many different things in science. Informatics, physics (particles, materials, space and other shit), durable energies, production and storage and transport of energy, calculus, data processing and exploitation, etc
And I really like change in what I'm doing, so if you're saying recruiters then will see me as an expert in one thing, unless I do PhDs all my life, it stinks.
Well I might have a lot more of searching to do... I'm thinking maybe informatics is the way to go for me, since it applies to many if not all things today...

I would ignore the academic requirements of those jobs unless you have no degree at all.
Experience trumps qualifications in almost all cases when it comes to industrial engineering unless you want to go into industrial research. You'll probably find quite a few older employees in engineering still don't have degrees at all.

Good luck with this.

While many universities may offer distance part time learning, this may not apply to what you specifically want. It may not even be relevant as implied by pm133. Given this, it may be best to figure out what your goal is and work backwards to your current position to see how it could be done, and how that plan works or doesn't work for you. You claim yourself a bad student for needing to see purpose in something. That's actually important to you and suggests a professional rather than academic approach to study suits you best. How specific can you be at what you are aiming at?

My goal is to get a job in which I get to think more. The job offers I'm interested in require experience and/or specifically oriented degrees, including PhD often.
I mainly need training and opportunities to learn new skills otherwise I won't be able to do these jobs (I get rejected all the time), though I admit it'd be nice if I could try a PhD, for personnal accomplishment or some such thing.

As for professional rather than academic, a thesis sounds a lot more than working to me in comparison to regular studying in which you just take courses and exams, which is precesily what I hate. My enginneering degree implied both courses and exams, but also a huge part in working in a company through apprenticeship, with a big presentation in the end (after 3 years, just like a thesis) and that kind of suits me. I mean way more than courses and grades: that means nothing to me. To put it in a nutshell I want to work for things that are going to be used.
I hope I'm being clear, english is not my native language.

This is very interesting, thanks for sharing this information.