Not quite. The "lo" refers to "it." If someone told you something you already knew, you'd respond with "Lo so," which literally means "I know it." In this example, "che sei ricca" is the "it," so "Lo so che sei ricca" would be like saying "I know it that you are rich," which is redundant and doesn't sound right. You'd only use "lo" with the verb sapere when there isn't already an object, and it might be weird to think of "that you are rich" as an object, but that's what you know, so therefore it's the object of the verb sapere.
Hey there, Fls5013 and thank you for getting back to me.
You are right: ❌"I know it that you are rich" is indeed wrong, since the sentence already contains an object ("that you are rich "), which renders the pronoun ("it ") redundant.
That, however, is the case in English and most other languages :) In certain languages, like Italian, Spanish and Greek, it is totally acceptable to have both the pronoun and the object of the verb to know in the same sentence:
saiche ti voglio bene? Lo
soche questo non è facile per te.
sabesque te quiero mucho? Lo
séque esto no es facil para tí.
ξέρειςότι σ' αγαπώ πολύ; Το
ξέρωότι αυτό δεν είναι εύκολο για σένα.
The word order, by the way, is identical in all three languages. The pronoun can always be dropped, but keeping it stresses the object: "You do know it, right? "
So, even though we couldn't have an original phrase like ❌"I know it that you are ...", I'm pretty sure that "Lo so che sei ... " is a correct translation to a phrase like the one under discussion here.
Thanks for the correction. I could be wrong (I am by no means a master in Italian), but I have a friend in Italy who I talk to in Italian only, and whenever she uses the verb sapere she doesn't use lo when what is known is specified, so I guess it's just weird to me that you can use both because I've never seen her (she's a native speaker) do it. It's probably a personal preference whether or not to use lo, and I'm sure if you said "Lo so che sei ricca" to an Italian they'd understand you.
I cannot say for certain, but I believe that "so" means "I know of something" or "I am familiar with something", whereas "conosco" is "I know this person" or "I am familiar with this person". In Spanish, it is the same with "se" and "conozco". The Spanish Saber is used for knowledge of objects or just information (i.e: I know you were late today; I know it is hot outside). The Spanish Conocer is used to confirm ones familiarity of a person or persons (i.e: I know that girl; I know the man in the red hat). I hope this helps.