What filter does a Vicks V4500 take?
None — this model has no replaceable wick or filter.
Vicks V4500, ultrasonic humidifier, tabletop.
Filter-free cool mist — the V4500's manual specifies cool mist (it is sometimes misdescribed as warm mist). No replaceable part.
Finding the model number on a Vicks
Model numbers are on the bottom of the unit, starting with 'V'. Juvenile models add 'JUV' (for example V3900JUV, the Starry Night projector model).
This entry exists so the answer is complete: if a store tries to sell you a replacement filter for this model, it is not a manufacturer part.