How can i get 3D world coordinates from 2D points

Hi, i just started in the computer vision world, and now iam researching about keypoints.

I just extracted keypoints and i cant get their 2d points in the image, that is easy, but also i want to know if its possible to get their 3d coordinates (x, y, z) in the world, so then i can use solvePnP and get the camera pose with keypoints.

I have calculated camera intrinsics, but i dont know the extrinsics.