I think around chapter 32? Though I recommend reading from the beginning since you get a clearer understanding of Xie Lian's thoughts in the novel.
i double checked my copies lol but i agree with the first comment ^^ about reading from the very beginning since it better explains Xie Lian, and Heaven, as well as info on the Calamities (and the Four Famous Tales bc i think they haven't shown it in the donghua yet??)
But there are two answers to your question! If you only watched to episode 12 (the finale) then you could start off at chapter 30! If you watched the special episode, you can start on chapter 32!
Again, highly recommend reading from chapter 1 hehe here's the link; https://www.novelupdates.com/series/heaven-officials-blessing/ personally i think the google drive download option is better since it compiles everything together
happy reading!
does anyone know what chapter of the novel to continue from the dongua/anime? ive just watched the animation and i rlly want to reas the novel