See corresponding blog post at http://natethedba.wordpress.com/finding-trigger-dependencies

FindTriggerDependencies_AuditTrailExample.sql

/* NJohnson9402 / natethedba.wordpress.com
Uses system catalog views and DMVs to find trigger table and column dependencies;
tailored as "audit trail" example, but applicable to most trigger situations.
Triggers always depend on & are a child object of the table on which they exist.
In this example, the predicate "OBJECTPROPERTY(trig.object_id, 'ExecIsUpdateTrigger') = 1"
restricts the view only to "ON/AFTER UPDATE" triggers; but you could easily extrapolate
to include the other types (INSERT, DELETE) as well, using the same model;
just replace 'ExecIsUpdateTrigger' with 'ExecIsInsertTrigger' etc.
*/
SELECT [Trigger] = trig.name
    , [On Table] = tab.name
    , [Key Column(s)] = col.name
    , [Audited Columns] = ''
    , [Key Pos] = icol.key_ordinal
FROM sys.triggers trig
JOIN sys.tables tab
    ON trig.parent_id = tab.object_id
JOIN sys.schemas sch
    ON tab.schema_id = sch.schema_id
JOIN sys.key_constraints kc
    ON tab.object_id = kc.parent_object_id
    AND tab.schema_id = kc.schema_id
JOIN sys.index_columns icol
    ON tab.object_id = icol.object_id
    AND kc.unique_index_id = icol.index_id
JOIN sys.columns col
    ON icol.column_id = col.column_id
    AND icol.object_id = col.object_id
WHERE OBJECTPROPERTY(trig.object_id, 'ExecIsUpdateTrigger') = 1
    AND trig.name LIKE 'AuditTrail%'
    --AND tab.name = 'Search-for-a-Table'
UNION ALL
SELECT [Trigger] = trig.name
    , [On Table] = tab.name
    , [Key Column(s)] = ''
    , [Audited Columns] = dep.referenced_minor_name
    , [Key Pos] = 999
FROM sys.triggers trig
JOIN sys.tables tab
    ON trig.parent_id = tab.object_id
JOIN sys.schemas sch
    ON tab.schema_id = sch.schema_id
CROSS APPLY sys.dm_sql_referenced_entities(sch.name + '.' + trig.name, 'OBJECT') dep
WHERE dep.referenced_entity_name NOT IN ('My_Audit_Trail_Table')
    AND OBJECTPROPERTY(trig.object_id, 'ExecIsUpdateTrigger') = 1
    AND trig.name LIKE 'AuditTrail%'
    --AND dep.referenced_minor_name = 'Search-For-An-Audited-Column'
    --AND tab.name = 'Search-for-a-Table'
ORDER BY tab.name, trig.name, [Key Pos], [Audited Columns]

Other object-property interrogators include "OBJECTPROPERTY(trig.object_id, 'ExecIsInsertTrigger')", "OBJECTPROPERTY(trig.object_id, 'ExecIsDeleteTrigger')", and more exotic ones like "OBJECTPROPERTY(trig.object_id, 'ExecIsTriggerDisabled')", "OBJECTPROPERTY(trig.object_id, 'ExecIsAfterTrigger')"; and you can even tell whether it's the first or last enforced-order trigger when there are multiple. You can really get crazy with triggers; I don't recommend it.