Basic question - referencing Field value

This may seem like a very basic question, but I need to pass the value of a field to a vb script:fnShowVal(xxxxxxxx)"Click to Show Value</A>
My problem is that I don't know what to replace the xxxxxx with in order to pass the Matter Number Value. I think it was referenced by value.Matter_Number_Value in previous versions but this no longer seems to work.
Could someone please provide info on how field values can be referenced?
Many thanks,

Bryan