How are these unvoiced consonants pronounced?

[Turama]

How do you pronounce a voiceless /n/([n̊]). Because of analogy, I would think it is pronounced like the unvoiced /w/, just adding /h/, so it sounds like /hw/([ʍ]). So is an [n̊] pronounced something similar like /hn/?
The second question is. Does [ɡ̊] (this diacritic means unvoicing) differ in any aspect from [k]? Is it kind of voiced but a little unvoiced? And if not, why are these kind of phonemes in use, at all (for example in german dialects) and not just the [k]?

[Kilanie]

[ɡ̊] is typically the same as [k]. It's used sometimes to indicate that the underlying phoneme is /g/. I think it may be used in some languages to indicate a third level of voicing, but I can't think of any examples right now.

[n̊] can be approximated by [hn], yes. However, [n̊] and [hn] are not the same thing (and neither are [ʍ] and [hw]).

[Imralu]

How do you pronounce a voiceless /n/([n̊]). Because of analogy, I would think it is pronounced like the unvoiced /w/, just adding /h/, so it sounds like /hw/([ʍ]). So is an [n̊] pronounced something similar like /hn/?

Yes. You basically put your tongue in the position for [n] and then blow air out through your nose.

The second question is. Does [ɡ̊] (this diacritic means unvoicing) differ in any aspect from [k]? Is it kind of voiced but a little unvoiced? And if not, why are these kind of phonemes in use, at all (for example in german dialects) and not just the [k]?

In describing German dialects, the distinction between [k] and [ɡ̊] is a fortis/lenis distinction, with [k] representing a fortis consonant and [ɡ̊] being lenis.

[zompist]

How do you pronounce a voiceless /n/([n̊]).

Exactly as you pronounce it while whispering.

[finlay]

Whispering is not the same as voicelessness, physiologically, although they sound similar. Voiceless nasals indeed sound just like you're breathing out through your nose – and I at least don't do this when whispering a regular nasal.

If you don't believe me, just try pronouncing 'vision' and 'fission' while whispering – they sound different because the normally voiced sounds are replaced by whispered sounds, but the normally voiceless sounds stay the same, in the larynx or glottis or whatever it's called. Voiceless is a wide open glottal state and whispering is a half-constricted state.

[Nortaneous]

Voiceless nasals are usually only pronounced partially voiceless, but I think languages vary in where the voicelessness goes.

Angami has actually-aspirated nasals, with positive VOT, but what I wonder is if the first part of the nasal gets voiced, as apparently happens in some TB lang I was reading about the other day where, say, /na/ would be [nn̥a].

[CatDoom]

This page (which is bizarrely frustrating to search for on Google) has audio examples of Hmong nasals, including voiceless nasals. If you navigate around you can find all of the phonemes in the language spoken by a couple of different speakers, which also include a number of tricky sounds like uvulars, prenasalized stops, and breathy voiced vowels.

[vec]

Say "hmm". That's a voiceless m followed by a voiced one. Practice until you can say it without the trailing voiced m. When you master that, repeat for other nasals.