“What HD gates would you say are most attuned to the frequency of resonance?”
&
“what activates it, and how could someone experience more of it?”

What do you mean by resonance, first.
and then perhaps also the frequency of resonance, second?

Mechanically (HD wise), or musically, or NewAgey those words do mean very different things.

Mechanically, resonance means same(ness), for instance a Transiting Gate is in resonance with your chart, aka you have the same Gate as the Moon is in right now. But then asking for the Frequency of this resonance has no bearing or meaning, it can not be determined.

Even if some people have connected frequency (measured in Hz) to I-Ching Hexagrams, something Robin Armstrong was into, but he seemed to have a different interpretation of where (Astronomically) which Hexagram was when seeing it from an HD perspective, so those frequencies may be in or for/about the wrong Gates. I made a comparison once here
https://www.mcha.nl/2013/04/17/i-ching-sequencing/

Musically then/thus, well yes if this above mentioned connection pans out, apparently Gates have (fixed/singular) Frequencies in Hz, and thus we can have resonance, by vibing/vibrating in the same frequency, and thus in resonance. Which would be the same as the top way, mechanically, same Gate = same frequency = resonance

NewAgey then, often if not always, when someone says ‘they resonate with something’, they simply mean they like it. With their mind. From a comparison point of view with a self made up moral measuring stick or adhering to someone else’ their made up comparison/measuring stick of mental liking. Being completely individual and ultimately subjective there is not one singular frequency to this then so called resonance, since the vibration -is- different for each individual. Funny how such homogenisation is therefor more diverse than the other 2 examples/angles. But also the reason why there are so many diverse and divergent/diverging schools of thought. No?

However still in none of these 3 can I detect ‘the frequency of resonance’

So do you mean it in yet another way/angle/experience, maybe/perhaps?

But then you also ask: “how could someone experience more of it?” I suspect NEwAgey after all, since this is one of few yet several modalities that seeks to manipulate the outer circumstances to achieve certain and very specific results, versus learning to live with what is. Seeking more (resonance or ‘frequency of resonance’ which is still undetermined what this can possibly be), just more, since more is more good, or something. Possibly.