are full backups always copied for daily tape jobs?

Full backups by default are and you can turn on incremental ones as well in the job configuration.  But tape synthesizes fulls from disk.

You can do incremental backups on tape.

But you to configure it in the incremental backup step of the tape job creation.

https://helpcenter.veeam.com/docs/backup/vsphere/backup_to_tape_incremental_pool.html?ver=120

tape synthesizes fulls from disk, That means with the daily tape job I always have the full backup, my question is which incremental backups are saved If I also back up the incremental to tape 

It depends what you set in the job.  Basically the entire chain will be saved to tape.

Read the link that was posted by Joe above which explains it.

For example, I make synthetic backups on Saturdays at the backup job.

what happens on wednesday If I select the incremental option in the tape job?
I have a full backup in the media pool full Backup and in the  incremental backup media pool, I have the incremental files from Sunday, Monday and Tuesday? correct?

yes, correct. But i would suggest also (with a Library in use), check the options when working with a GFS pool - make things imo easier:

GFS Backup to Tape - User Guide for VMware vSphere (veeam.com) and Step 4. Specify Media Set Options - User Guide for VMware vSphere (veeam.com)

THX Dynamic

i found the Answer in GFS 

Usually, daily media sets do not contain full backups as daily backups are mostly used to keep day-to-day incremental changes. To complete the backup chain they use the periodic full backup stored in the weekly or monthly media set. We recommend to enable the usage of weekly media sets or carefully consider the retention plan.

glad we could guide you in the right direction 

i typed wrong, i wanted to give your answer as the best answer, unfortunately i can't open the topic again, sorry Dynamic

Great to hear you resolved the issue.

no worries, also Chris and Joe contributed to this. We are here to help.