You will have to use sp_executesql to execute it:

EXEC master.dbo.sp_MSForeachDb 'USE [?]

IF "?" NOT IN (''master'',''model'',''msdb'',''tempdb'')

BEGIN

SELECT ''?''

DECLARE @query nvarchar(50)

SET @query = ''CREATE SCHEMA [T_schema]''

EXEC sp_executesql @query

END

'