Could orthodontic cement be able to stick on brace brackets onto retainers?

Yes, but why?: This technic is sometimes used to do 'direct bonding' (a method of applying braces to teeth-- the retainer is removed as part of the process), but if you were doing this yourself i would not understand why.

Perhaps: You can bond an orthodontic bracket onto a false tooth attached to a retainer that's there to replace a missing natural tooth. You cannot readily bond to the metal parts of retainers.

It is possible: However, treatment decision should be made after discussion between you and your Orthodontist/Dentist.