How to list permissions on a schema?
Using the accepted answer from List schema permissions, this would probably give you what you want.

--demo setup
CREATE DATABASE listschema
GO

USE listschema
GO

CREATE SCHEMA TestSchema
GO

CREATE USER TestUser WITHOUT LOGIN
GO

GRANT SELECT
    ON SCHEMA::TestSchema
    TO TestUser

DENY INSERT
    ON SCHEMA::TestSchema
    TO TestUser
GO

--The actual query
SELECT state_desc
    ,permission_name
    ,'ON'
    ,class_desc
    ,SCHEMA_NAME(major_id)
    ,'TO'
    ,USER_NAME(grantee_principal_id)
FROM sys.database_permissions AS PERM
JOIN sys.database_principals AS Prin
    ON PERM.major_ID = Prin.principal_id
        AND class_desc = 'SCHEMA'
WHERE major_id = SCHEMA_ID('TestSchema')
    AND grantee_principal_id = user_id('TestUser')
    --AND    permission_name = 'SELECT'
GO

--cleanup
USE tempdb
GO

DROP DATABASE listschema




| state_desc | permission_name | (No column name) | class_desc | (No column name) | (No column name) | (No column name) |
|------------|-----------------|------------------|------------|------------------|------------------|------------------|
| DENY       | INSERT          | ON               | SCHEMA     | TestSchema       | TO               | TestUser         |
| GRANT      | SELECT          | ON               | SCHEMA     | TestSchema       | TO               | TestUser         |