This is for a Moto G (Android OS vers. 4.4.4 and vers. 5.1) and was the same on Moto E, but didn't apply to my LG Volt, so it's likely to be different for other phones.

I recently had an issue with some pictures not getting uploaded to the cloud and thought it might be because I didn't have Google Sync on. But when I checked to see that it wasn't on, I couldn't find where to turn it back on.

I searched on Google and what I found was that the location to turn on Google Sync changed from Android v. 4.4.4 to 5.1.

In order to turn Google Sync on/off on v. 4.4.4:

Select Settings -> Data Usage, then press the 3 dots (menu) and select or unselect the "Auto-sync data" checkbox.

In order to turn Google Sync on/off on v. 5.1:

Select Settings -> Accounts, then press the 3 dots (menu) and select or unselect the "Auto-sync data" checkbox.

If you select Google, it's there that tells you your Google Account name and whether sync is on or not and then you can select your Google Account name and you'll see toggles to turn on/off individual items to sync e.g. Gmail or Contacts. This will only show if you have "Auto-sync data" checked.

I found it confusing and not intuitive at all.

Apparently, it was in a confusing location in 4.4.4, so Google moved it, but not to a place that's less confusing.