Day One Mac keyboard shortcuts:
Command Function
Command-N New Entry
Shift-Command-N New Entry in Window
Command-1 Timeline View
Command-2 Photos View
Command-3 Map View
Command-4 Calendar View
Command-B Bold selected text
Command-I Italicize selected text
Control-Shift-D Menu bar entry (customizable in Settings)
Left/Right Arrows Previous/Next pane
Up/Down Arrows Previous/Next Item in a List
Command-E (or Command-Return) Toggle Entry Edit Mode (Save/Sync)
Command-F While in an entry this will search text
Command-Shift-F Search all data in Day One
Command-J Open Journal Picker
Command-T Open Tag Menu
Command-comma Preferences
Shift-Command-L Lock Journal
Command-Control-F Toggle Full Screen
Command-K Create Link (from selected text)
Command-Shift-T Insert Checklist
Command-Shift-J Toggle Journal Sidebar
Search commands
Below are screen shots to show how the different search shortcuts will appear in the app.
Command-F While in an entry this will search text

Command-Shift-F Search all data in Day One

Day One iOS keyboard shortcuts:
Command Function
Command-N New Entry
Command-Return. Toggle Entry Edit Mode
Up/Down Arrows Previous/Next Item in a List

See More: Mac Keyboard Shortcuts