If you're working on a visual effects (VFX) project in Nuke and need to attach a 3D object (obj) for compositing, here's how you can do it. First, ensure that you have the 3D scene set up in Nuke. Then, import your obj file by adding a ReadGeo node and selecting the obj file from your system. Once the obj file is imported, use a Scene node to place and position the obj in the 3D environment. You can then connect the Scene node to your 2D image or footage using a ScanlineRender node to see how the obj integrates with the scene. If adjustments are needed, you can use a TransformGeo node to modify the position, scale, or rotation of the obj within the scene. Finally, ensure that your lighting and shading settings match the environment to achieve a seamless integration. By following these steps, you can successfully attach an obj in Nuke for your 3D compositing and VFX work.