Could depend on the railroad. In some cases, railroads ordered first generation diesels without a bell, and then mounted the bell from a recently retired steam engine on the cab roof or on the long hood.
Railpictures.net lets you search by loco type.
I don't know if this is usual but it's right behind the left front steps in this VO-1000
Henry
COB Potomac & Northern
Shenandoah Valley
Where was the bell usually located on Baldwin switchers, such as VO series?