Search for a field in all objects

SOQL/SOSL won't help you here. You can, however, write a query using the Tooling API like this:

SELECT Id,TableEnumOrId FROM CustomField WHERE DeveloperName = 'Owner'

The easiest way to do this is to open the Developer Console, click the Query Editor tab, check the "Use Tooling API" checkbox, and type in the query. Note that you do not include the __c when querying this table.

For custom objects, you'll get a custom object ID. You can see the object by using the standard URL for an object:

https://<domain>.salesforce.com/01IC0000000XXXXXXX