Is there anyway to teach my SBT pup (4-5 months) to give a warning bark? She has done before - but only once...

Warning bark for what reason - you havent been very clear
warn an attacker/burglar off ? Warn you she wants the loo?

:D :D :D

Sorry - warning barks for people / burgerlers... maybe just a bark to let me know there is someone @ the door... i dont know if its possible to teach / encourage it - it might be done to the personality of the dog.... I though sbt's were quite protective...

Think Staffys are not the best dog in the world with regard to protection . Protecting their toys from another dog then yes, ;)  but they are not naturally people aggresive .
Do you want pup to be a hearing dog or a guard dog ?
My last Staffy never barked but Gus will growl if he hears unaccustomed noises at night.

It is extremely easy to teach a dog to bark, unfortunately not many people have mastered the art of teaching it to shut up :(

All you have to do is frustrate the dog eg wave its dinner about and not give it this will usually get the dog frustrated enough to bark.  Once it does this reliably for food you can add a command and hey presto.

She's still very young to start barking - it will come, especially if you reward and praise her when she does do it of her own accord.....