Outlook Notes and iOS Notes do not automatically migrate to Gmail. However, there are options for moving them manually.
NOTE: When referring to "Notes," we are referring to the Outlook Notes feature, NOT Contact notes, which do migrate. Contact notes are notes taken about a given contact.
To migrate your Outlook notes, open your old Outlook account (available for a period of time after the migration) and follow the below instructions:
Navigate to your notes folder in Outlook. Select all notes by clicking on the top one and then Shift+Clicking on the bottom note. Click File, Save As.
Choose where you want to save the file, type in a name, and make sure "Text Only" is selected. Click Save. Now you will have a text document with a list of all your notes from Outlook.
If you would like your notes online, you can copy and paste them into Google Keep.
For iOS Notes, How-To Geek has a great article on making them sync with Gmail. Read it here.