Can you save all your open tabs at once?
Yes. File > Save all in Jotter by Zaweba saves every tab that has a file in one go, while unsaved notes are kept safe by session restore.

Yes. In Jotter by Zaweba, choose File > Save all and every tab that has a file behind it is saved in one go. You don't have to visit each tab and press Save. Tabs that are new notes without a file are left as they are, and Jotter keeps those safe anyway, bringing them back each time you open it.
That split is worth understanding, because it explains why Save all is quick and why it never asks you a string of questions.
Files and notes are different
A tab in Jotter is one of two things. It is either a file you opened or saved, with a name and a place on disk, or a jot: a note you started with Ctrl+N and never saved as a file. A jot is named after its first line so you can tell it apart from others.
Save all deals with the first kind. Each file tab is written back to its own file, in the encoding and with the line endings it already had. A dot on a tab shows unsaved changes, so after Save all the dots on file tabs disappear.
Jots don't have a file, so there is nowhere to save them without asking for a name. Rather than pop up a Save as dialog for each one, Save all leaves them alone.
Why unsaved notes are still safe
Jotter writes every tab, saved or not, to its own session folder in your user profile, a few seconds after each change. Close the program and nothing is asked; open it again and every tab is back as it was, unsaved notes included. A crash or a power cut loses almost nothing, because the text was already on disk.
So you don't need to turn every jot into a file. Many people keep phone numbers, half-written replies and scratch lists as jots for days or weeks. When a jot is worth keeping as a file, open its tab and use Save as.
When to use Save all
It is handy after editing several files together, such as a set of settings files or a few notes you keep as text files in a folder. Make your changes across the tabs, then Save all once at the end.
It is also a good step before something else needs to read those files. If another program, a backup or a sync folder is about to pick them up, saving them all first makes sure it gets your latest edits, not the copies from before.
Saving one tab at a time
File > Save saves the current tab, and Save as lets you give it a new name or location. Closing a single tab with unsaved changes asks first, because that is the one action that would throw changes away. Closing the whole window never asks, since the session keeps everything.
A tidy routine
A routine that works well is to let jots pile up through the day, Save all whenever you have edited real files, and now and then go through the jots: save the ones worth keeping with Save as and close the rest. Jotter by Zaweba then stays a clean notepad with nothing ever lost along the way.