Mosaico displays editing icons depending on the nature of the text. However when text is to be edited the Format drop down does not include the ability to create bullets or numbered lists. Where are the edit icons configured in Mosaico templates?
I opened Word, pasted the text I wanted bulleted, then bulleted it, then copied it and pasted it into Mosaico template. The bullets held.
To add bulleted and numbered lists to the Mosaico editor, install the Mosaico Toolbar Editor (com.ginkgostreet.mosaicotoolbarconfig) extension.
Then go to Administer > CiviMail > Mosaico Settings, and edit the Mosaico Toolbar Settings field and insert
bullist numlist after
Hopefully this might be incorporated into CiviCRM Mosaico one day so that it wouldn't be necessary to install another extension but for now this is how to do it.