How to add part in eagle board that doesn't have corresponded in the schematic "jumpers"?
To figure it out you need to understand how EAGLE works. Each device you find in library consists of three components - package, or board footprint with pads (through hole or SMD), symbol with pins, and correspondence between package and pins.

You can add package to board without adding symbol to schematics, but you will not be able to connect to its pads properly, and DRC will give you "overlapping" errors.

The right way is to add jumper to schematics, connect its pads respectively, and wire pads at the board level with tracks. All other ways is hacking, which may lead to


your mistakes, and tool will not be able to advise you what is wrong;
errors in DRC, and you may not be able to find the issue quickly.


EAGLE is a powerful tool, but please refrain misusing it. You will spend much more time figuring out why EAGLE gives you errors, or why your board does not work properly. Just follow rules and design board the way EAGLE supports.

Thus the answer is

You must add jumper to schematic, and wire it as needed at both schematic and board levels.