18.36What SOQL should you memorize?

These three:

Normal lookup

SELECT Id, Name
FROM Account
WHERE External_Customer_ID__c = :customerId

Child → Parent

SELECT Id, FirstName, LastName, Account.Name
FROM Contact
WHERE Account.Customer_Status__c = 'ACTIVE'

Parent → Children

SELECT
    Id,
    Name,
    (
        SELECT
            Id,
            FirstName,
            LastName
        FROM Contacts
    )
FROM Account

That's enough to demonstrate real familiarity.