Whats this position called

In English this would be called kneeling, but that is a broad term that would apply to different positions as well. Any position resting on the knees is likely to be called kneeling in English.

Technically the word for it is "seiza", but few people will actually understand what you're talking about if you say that. I'd just call it "kneeling" for simplicity's sake.

Seiza , if you wanted to know the original name.

Kneeling. There is no other specific word in English, but there probably is in Japanese.

If you’re on your knees you’re kneeling. If your butt is on the floor you’re sitting. Seiza is not an English word.

It is likely most Americans would call Seieza 'kneeling'. Some may call it sitting. There are several terms for sitting cross-legged.

Japakneeling.

Kneeling on the ground.

If you want to be more specific than kneeling, it sitting on your heels.

We don't have a specific word for 正坐 in English because we don't sit like that. The closest approximation would be kneeling or "sitting on one's knees". Just like you wouldn't have words for very specific American or Western customs, we don't have words for Eastern ones.

Kneeling. If I wanted to be specific about this pose, I'd borrow the Japanese term, Seiza. People who are unfamiliar with Japanese culture are unlikely to know what it means without explanation. "Japanese-style kneeling" may work, but once again, requires at least passing familiarity with Japanese culture. People don't tend to sit like this in native English speaking/western countries, growing up you learn to sit cross legged, so it just isn't named. As adults, people are likely to sit leaning against something, sit with their knees to their chest or sit cross legged before they sit like this.

When I was growing up we called it sitting Japanese style!

Maybe I’m weird, but I call this “kneeling down” to distinguish it from the version of kneeling where the hips are over the knees (and which I might sometimes call “kneeling up,” but I’m pretty sure that’s a me-thing).

People have already answered, but you should look up what a W-sit is. It’s similar to the position you described with your butt touching the floor

If you're sitting with your knees bent back and out which I assume is what you're talking about for the second thing you mentioned on your post, like kneeling but legs splayed out, while most people would call it kneeling, the term in medical/therapeutic circles is W sitting because the legs form a W shape. That is technical jargon though, not commonly used language

Kneeling and cross-legged.

Kneeling is what most people would call it, but that would also cover a bunch of other positions. Maybe someone would say "sitting on your heels" but that is kind of specific and is more of a description of the position rather than a specific word -- there isn't really a perfect 1-to-1 translation of the word 正座 into English.

Neither has an assigned single word in English. I use seiza because I’ve done some Japanese martial arts but not everyone knows the word.

Seiza “say za”

Side by side

"Kneeling on both knees" / "sitting with legs bent to the side" (if legs are to one side of the body with butt on the floor) or "sitting with legs bent to either side" (if there's one leg on each side of the body with the butt on the floor) There's no concise term to convey either position in English.

For the second part of your question, when your knees are forward but legs are angled and butt is on the floor its known as W Sitting (as the legs make a W shape)

we dont have a singular word for it (that i know of), I would describe it as "sitting on my knees", i think "kneeling" while not too inaccurate evokes a different image in peoples minds, where the person isnt sitting but instead more upright like a catholic praying in a pew.

id call this "sitting on your knees" for me, "kneeling" gives the mental image of getting down on one knee

正座 (seiza)

The Takeshi Castle Earthquake simulator position. Sorry, I don't know, I'd guess you'd say "kneeling".

kneeling, generally. I'd call sitting with your legs out "W-sitting" or something similar

That's japanese seiza style

kneeling would be general

In case you were looking for a meditation / yoga posture, it might be Vajrasana or Virasana

if i was trying to tell someone to sit like this (i know it’s not very PC but) i would be telling them to kneel in an asian way/ kneel and sit on their heels

Celibacy. It’s the dullest illustration in the Karma Sutra.