How do you list the primary key of a SQL Server table?

This is a solution which uses only sys-tables.

It lists all the primary keys in the database. It returns schema, table name, column name and the correct column sort order for each primary key.

If you want to get the primary key for a specific table, then you need to filter on SchemaName and TableName.

IMHO, this solution is very generic and does not use any string literals, so it will run on any machine.

select 
    s.name as SchemaName,
    t.name as TableName,
    tc.name as ColumnName,
    ic.key_ordinal as KeyOrderNr
from 
    sys.schemas s 
    inner join sys.tables t   on s.schema_id=t.schema_id
    inner join sys.indexes i  on t.object_id=i.object_id
    inner join sys.index_columns ic on i.object_id=ic.object_id 
                                   and i.index_id=ic.index_id
    inner join sys.columns tc on ic.object_id=tc.object_id 
                             and ic.column_id=tc.column_id
where i.is_primary_key=1 
order by t.name, ic.key_ordinal ;

SELECT Col.Column_Name from 
    INFORMATION_SCHEMA.TABLE_CONSTRAINTS Tab, 
    INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE Col 
WHERE 
    Col.Constraint_Name = Tab.Constraint_Name
    AND Col.Table_Name = Tab.Table_Name
    AND Constraint_Type = 'PRIMARY KEY'
    AND Col.Table_Name = '<your table name>'

It's generally recommended practice now to use the sys.* views over INFORMATION_SCHEMA in SQL Server, so unless you're planning on migrating databases I would use those. Here's how you would do it with the sys.* views:

SELECT 
    c.name AS column_name,
    i.name AS index_name,
    c.is_identity
FROM sys.indexes i
    inner join sys.index_columns ic  ON i.object_id = ic.object_id AND i.index_id = ic.index_id
    inner join sys.columns c ON ic.object_id = c.object_id AND c.column_id = ic.column_id
WHERE i.is_primary_key = 1
    and i.object_ID = OBJECT_ID('<schema>.<tablename>');