Hi Scott,
With respect, I think you are misunderstand what attributes actually are. Another word for them would be "properties". CIC has two types of these, Interaction and Directory Services (DS).
When a call comes in (or any interaction for that matter) an object is created (Interaction1) which can be thought of as being a bit like a bucket. Inside that bucket are the attributes. Some (most) of these are automatically set by the system (DNIS, ANI, Line etc.) You can think of them as being like pieces of paper with information in them. The object, for all practical purposes IS the call, and so it goes with the call wherever the call goes.
Ok, so far so good. Custom attributes are ones that you add. There are two primary ways to do this (there are others, but bear with me!). The first is in Attendant. You can directly set an attribute using the Set Attribute operation, or some of the other operations can be configured to set an attribute as well (for example Caller Data Entry). Prior to this step being executed, the attribute needn't exist (although it can). The secon place you can access attributes is in a Handler, where you can both get and set them.
So, in your scenario, you could prompt the caller for their SSN in Attendant and assign the response to an attribute. Effectively, what has happened is that the information has been written on a new piece of paper and put in the bucket. When you then execute your handler, (presumably using Run Subroutine?) you are given Interaction1, which is essentially the bucket. That means you can use get attribute to retrieve the value into a variable. In terms of 'where do i tell the Handler what it is looking at when it is looking for "MOH_LoanCount"', it looks in the bucket. How does it get there? You put it there!
For the sake of completeness, DS attributes are any property set on an object in IA. If you need to store an additional information, you can do that on the "Custom Attributes" tab. Say, for example, you wanted to inform the caller what color the agent's eyes were (keep with me here!) then you could store the eye color in a custom attribute for the agents. In a handler you could pull the information from the agent's DS object to read it out to the caller.
In all honesty, I would recommend taking the Handlers class.
HTH