In Trailhead we have the query to get the Contacts for the Account named "SFDC Computing", with an inner query.
SELECT Name, (SELECT LastName FROM Contacts) FROM Account WHERE Name = 'SFDC Computing'
It works fine for my purposes. "Contacts" is the name of the relationship, per Trailhead. So, I went to Object Manager and examined the Account object's "Fields and Relationships". There is nothing named "Contacts"!
In general, how do I get the name of the relationship, for use in similar SOQL queries?