As far as I know they're just different parts of speech.
Investiture is a noun: it's the state of something being Invested with energy from the Spiritual Realm, or the energy that is contained in someone or something.
Invested is an adjective: it describes a noun that has Spiritual Energy in it.
Investing is a progressive verb: it describes a noun being imbued with Investiture, by whatever mechanism.
Investiture is used by Taravangian to describe the effects of advancing people through the Nahel bond: "Care must be taken to avoid placing these subjects in situations of powerful stress unless you accept the consequences of their potential Investiture." (WoR, page 935). He is describing the risk of people becoming imbued with energy from the Spiritual Realm by developing the Nahel bond.
Invested is used by Zahel to describe a Highstorm: "One of those storms had come, Invested to the hilt and looking for a place to stick it." (WoR, page 398). Zahel is describing the Highstorm as being filled with energy from the Spiritual Realm.
I don't recall seeing the word Investing used this way in a Cosmere novel offhand, so I can't give an example of that one.
