I've noticed some dark bumps on my chest kind of look like black heads but when i tried squeezing them nothing comes out. what can it be ?

Black heads: they may be normal skin gland the secrete oily substance called sebum. You may not be able to squeeze them out. If they are not growing or bother you, may be left alone. If they bother you please get them checked out by your physician

Unknown.: This could be a great number of things. In this case, direct observation would be extremely helpful. They could still be black heads (comedones). This would be more likely if they were located in the midline of your chest, e.g. over your sternum (breastbone). Other possibilities would be skin tags, seborrheic keratosies, mollluscum contagiosa, sebaceous hyperplasia, keratosis pilaris, etc.

Hyperpigmented: Papules may show folliculitis or acne. Do not squeeze, see your PCP

Cannot cay: It is hard to say what you have on your chest. You may have cysts that are deep enough that you cannot squeeze the contents out. I would see either your primary care physician or dermatologist.