There are a couple of ways to verify if your data is synced to Day One Sync.
In the settings, the sync status will show when sync was last updated.
iOS – go to Day One > Settings > Sync Status
macOS – go to Day One > Settings > Sync. There is also a sync status icon below the list of journals in the journal sidebar on Mac.
Android – go to Day One > Settings > Sync
Day One Web (beta)
Day One has recently launched on the web as a public beta. Users can sign in to their account and view journal data for each journal and statistics for their account. Please go to https://dayone.me/login to sign in.
Once signed in, you will need to enter the encryption key for encrypted journals. See here: https://dayoneapp.com/guides/day-one-on-the-web/getting-started-on-the-web/#adding-your-encryption-key
Once signed in, you can view your journal data. Click a journal on the sidebar to see Journal Statistics on the right side. Click All Entries to view statistics from all journals.
Click Settings below the list of journals to manage your sync account.
Sign out from the Settings menu when you are finished.