You can see the defaults and their definitions with this query:
select object_name(o.parent_object_id) as ObjectName
, cl.name as ColumnName
, o.name as DefaultName
, c.text as DefaultDefintion
from sys.syscomments c
join sys.objects o on c.id = o.object_id
join sys.columns cl on cl.object_id = o.parent_object_id AND cl.default_object_id = o.object_id
where o.type = 'D'
Edited to find user defined types:
DECLARE @MyTable AS dbo.MyTableType;
select object_name(o.parent_object_id) as ObjectName
, cl.name as ColumnName
, o.name as DefaultName
, c.text as DefaultDefintion
from tempdb.sys.syscomments c
join tempdb.sys.objects o on c.id = o.object_id
join tempdb.sys.columns cl on cl.object_id = o.parent_object_id AND cl.default_object_id = o.object_id
where o.type = 'D'