Can my employer read my notes if I use their Wifi?

I have "Colornote" app in my android device and I'm using that app for many years. I write my passwords and many other personal things. My workplace has wifi and I use it regularly. Often my notes gets synced when I use that wifi. Can my employer read my notes? Colornote says they use AES encryption. I don't understand what it means. Many times, I use public wifi too. When I use public wifi, can they read my passwords and personal notes? Also can they read other word and google doc app documents that I have saved in phone and get synced when I'm online? And if answers of the above questions are yes, will installing and using Norton360 VPN app secure my notes? Thanks.