I still don't get what a Eunuch is :)

Someone whose penis has been cut off for specific social roles like in the ancient times.

An Eunuch is someone who works in the palace in ancient Korea.
In this case, they are kind of like servants and they usually run the palace's daily affairs.
They can even potentially become political advisers to the emperor.
And yes, one of the requirements to being an eunuch is that you have to be castrated.

so how does this eunuch still have it? do they cut off the whole penis, how do they pee
i'm sorry i'm genuinely confused ┗( T﹏T )┛

Only the balls are cut not the penis.

Only the balls are cut not the pe nis.

so that means they cant impregnate someone ? but can they get a boner, have sex and all??

I don't think they can reproduce if their testicles are cut off., some I think are celibate while others are not. You can actually research about it if you're really that curious.

There were 2 types of castration in the past. The one where only the balls are cut off and the other (the more common type in ancient East Asia e.g. China, Korea, Japan) was they cut both the balls and the shaft and left only a little portion to let the pee pass. End result was like an engorged female genitalia.
The object was to prevent their ability to impregnate any women in the palace without Emperor's consent as all women including even the maids belong to the Emperor. If they were on the Prince's household they belong to the Prince.

However I nvr heard of Revived Eunuch term as in this comic. Since it's not like what had been cut off could grow back like some octopus' tentacles (￣∇￣") so
I have read once that sometimes the cut off penis, if done when they were very little, can still grow a bit more but only when it wasnt cut off completely and it wouldn't grow back to normal size.

I'm not sure how in the picture the Eunuch had full normal size dick with balls and no function is lost. My guess is he probably never castrated before?