More than focusing on other servers that link to your current server, I would worry about applications. In complex environments, some applications may be out of control and keep pointing to your old server.
In these cases, this is the plan I am using:
- install the new server with the same instance name as the old one
- migrate all server objects, including logins and everything else
- switch off or rename the old server
- add a CNAME in your DNS to point the old server name to the new
This way, you don't have to worry about linked servers, ETL jobs or applications still pointing to the old server.
Obviously, this assumes that you already have tested everything to be compatible with the new version.
Based on your comments, if you still want to discover incoming linked servers, you can register all your servers and run a multi-server query like this:
where product = 'sql server'
and data_source = 'your sql server 2005'