The publication 'My_publication' doesn't exist?
You need to run that procedure in the context of the publication database (the database that is the source of the data you wish to replicate).  You can do that with a USE statement:

USE [YourDatabaseName];
GO

EXEC sys.sp_publication_validation 
    @publication=ReplicationFaouzi,
    @rowcount_only=0,
    @full_or_fast=0,
    @shutdown_agent=0


If you're unsure of which database is the publication database, you can run this query to find which databases are configured as publishers:

SELECT [name] FROM sys.databases WHERE is_published = 1;


Once you have the database name from that query, you can run this to see the name of the actual publications that should be passed to sp_publication_validation.  In your case, the publisher is named Guichet, so you'd run:

USE [Guichet];
GO
EXEC sp_helppublication;


This will give you the value that needs to be passed to the @publication parameter.



Note that all of the above is written in the context of transaction replication (which is what the original question was about).  Different steps are required for different types of replication.  

There is a great "information gathering" script on the Microsoft Docs website that walks through getting info on distributors and publishers when using different types of replication:

Distributor and Publisher Information Script