This is a paid asset, but now you can download UV Inspector Free.
Detail this asset from Unity Store: Original Link
UV Inspector v1.2 (Latest version)
Utility to preview UV coordinates of the mesh.
– UV1, UV2, UV3, UV4
– Skinned Meshes
– Vertex Colors
– Isolated Texture Channel Preview
– Ability to save an image of the UV layout
– Ability to inspect uv values