How do I see what Reference properties and Value properties I can address in GetComponent in C#?

Newbie question but couldn't find an answer anywhere!

I'm making a script that generates a gradient texture procedurally to apply to a panoramic Skybox, so I can change the colors of the sky later.

I followed this tutorial for the texture script: https://catlikecoding.com/unity/tutorials/noise/

My Main Camera has a script called 'TextureCreator' and a 'Skybox' component. The 'Skybox' component has a property called 'Custom Skybox' in the Inspector which references the 'Skybox Material' currently. I want to do the following: GetComponent().CustomSkybox.Spherical(HDR) = myTexture; But 'CustomSkybox' isn't a property with a definition!

My question: How do I see what property I need to reference in C# to reference, for instance, CustomSkybox, and later reference the Skybox material's texture so I can change it?