Genuine question: What does Jiraiya do if Itachi had decided to use Amaterasu on him right in this moment?
Jiraiya didn't know about Amaterasu at this point since he didn't know what it was when Itachi used it to escape frog stomach. Yes, Jiraiya can draw a fire sealing scroll but taking out a scroll and then drawing detailed symbols seems quite difficult when you are burning to death (plus the scroll might get burned before Jiraiya can draw the fire seals on it lol). Plus can't Itachi see Jiraiya drawing and attack again to stop this? This is before Itachi used his second Tsukyomi on Sasuke so it's safe to say he had enough chakra to use amaterasu multiple times like we saw a half dead Itachi do against Sasuke.
Jiraiya didn't know about Amaterasu at this point since he didn't know what it was when Itachi used it to escape frog stomach. Yes, Jiraiya can draw a fire sealing scroll but taking out a scroll and then drawing detailed symbols seems quite difficult when you are burning to death (plus the scroll might get burned before Jiraiya can draw the fire seals on it lol). Plus can't Itachi see Jiraiya drawing and attack again to stop this? This is before Itachi used his second Tsukyomi on Sasuke so it's safe to say he had enough chakra to use amaterasu multiple times like we saw a half dead Itachi do against Sasuke.