In Spanish, the sentence is actually saying something like 'I have figured it all out." There is something--"lo"--that I have figured out, and I haven't just figured it out in part, I have figured out "all" of it. Combining 'todo' with 'lo' is pretty common, because 'todo' has a strong sense of being an adjective in Spanish and adding a 'lo' makes it into a noun.
Seems to me like it makes more sense to translate this as "it ... all" ("I have determined it all") than as "everything." Though the difference in meaning is the thinnest of shades, I have to admit that I sleep better when someone can explain these things to me. Muchas gracias.
There's no 'of' in this sentence, thus incorrect.
Lo here is talking about 'todo' as a direct object. The verb is asking, Who/what has been determined? And the answer is 'todo'. Look up Professor Jason on Youtube. He has great videos describing the usage of direct and indirect objects and pronouns. He speaks both English and Spanish so it's good for listening practise also. Buena suerte!
Translation is not always literally word for word. Otherwise, we English speakers would accept "It I have discovered all." Consider the phrase "el sombrero de Juan," which is usually translated to "John's hat." Use of function words like prepositions and conjunctions is different in each language. The phrase "all of it" sounds much more natural to a native English speaker.
I used 'figure out' as a translation for 'determine,' and got it wrong. I'm OK with that, since it's not really a standard translation. But how would you translate 'figure out'? My search engine says 'calcular,' but can you really use that to translate the sentence 'I have figured out how to fix my marriage,' for example?