How to get texture data using textureID's in openGL

You are probably looking for glGetTexImage (see https://www.khronos.org/opengl/wiki/GLAPI/glGetTexImage for further information).

Before using glGetTexImage, don't forget to use glBindTexture (https://www.khronos.org/opengl/wiki/GLAPI/glBindTexture) with your texture ID.