You can manually run and monitor the validation using the replication monitor.

Open the replication monitor

Open the subscription you wish to validate

Chose the menu option "Validate Subscription"

You should probably select the "rowcount and checksum" option

Then the next sync, it will validate, and show the results in the subscription monitor window, and flag any articles that fail. You can start the sync manually if you like.

If you do have errors, sorting them out is another story... You can do it, but it is a slow manual procedure. I've had to do it a number of times when various client envs have left machines expire and I've had to get them resubscribed without initialisation so we don't lose transactional data. It is do-able, but slow...