My girlfriends ex partner is giving his child excessive salt, does it cause nosebleeds and shakes?

No: Nose bleeds are common in young children and mostly hereditary. High salt diet may lead to hypertension.

Depends: If it is excessive table salt, that would not cause nose bleeds, but may make the child more prone to hypertension. If the "salt" is not usual table salt, it would require evaluation.

Define "excessive" ?: If he just allows/encourages the child to salt their food beyond what you think wise, it is a relatively minor issue. It would not cause symptoms but may set them up to salt crave/be hypertensive later in life. If he is feeding the kid a salty brine every day this could mess up its metabolism to the point it kills them. This should prompt a call to the CPS hotline as suspected child abuse.