"Today I see better."
Translation:Oggi vedo meglio.
"meglio" is actually comparative of "bene" not "buono":
bene is an adverb and expresses a positive judgment. It modifies a verb. Lei cucina bene ---- Lei cucina meglio
buono is an adjective that expresses a positive judgment, usually it refers to the aspect of the content, of the quality: Il studente è buono. --- Il studente è migliore.
I think that Ci vedo meglio. should be accepted as well and it is even better in this context because:
vedere → mainly the transitive "to see (an object)" ( i.e. to perceive something with my sight ), and at most formally we could also use it to say "to be able to see" ( ability ) as Duolingo means here;
veder-ci →the intransitive "to be able to see" ( ability ), called "verbo procomplementare" as well as "pronominale" because of the clitic -ci that also changes the syntactic meaning of the simple vedere ( but this particle has many other functions according to the case, be careful )
So the second solution is common and natural for this phrase.
Unless you need to say "I can see better" in English...but I don' t think so because I've found translations where "I see better = Ci vedo meglio", that is to say the modal verb " can" is implicit.