I want to know how do I change the coordinates of the copy's origin point on the page.

I created two projects in Krita, one with the pixel dimensions of an A4 sheet and the other with the dimensions of 8x8 pixels.

When I copied the drawing layer I made on the 8x8 page, a yellow square 8x8 px, and pasted the original coordinate on the A4 project page, it was not in the center of the page but at the 0.0 coordinate of the page.

I need all copies inserted in the A4 project to have their point of origin in the center of the page or in the center of the selected area.

What do I do that with?

The only way I can think of is to use Edit -> Paste at Cursor which needs some setting up to make it useful.
You need to make a shortcut for this because it doesn't have one in the default shortcut settings.
Strangely, the Ctrl+P shortcut is for Print which doesn't exist as an operation so you can get rid of that from the Print shortcut and use it for Paste at Cursor.

Then make a centre marker layer on your A4 image and zoom into that marker and place your cursor on it and do Ctrl+P. The centre of the pasted image will be at the cursor location. (This is a surprise because I'd have thought that the top left origin of the pasted image would be at the cursor location.)

I can't think of a method to paste at the centre of an arbitrary selection, unless you're very good at placing the cursor there yourself.