Desimeter
Litres.
stock keeping unit
No difference. A unit of stock is called a share.
Capacity isn't a unit at all. It's a characteristic, or a property of an item, which can be measured in whatever suitable unit. Capacity of batteries is measured in amp hours. Capacity of a gas tank can come in either liters or gallons.
The "specific heat capacity" is simply the heat capacity per unit - it might be per mass unit, per volume unit, or per amount of moles.
Liter is a unit of volume (or capacity). Gram is a unit of mass.
Milliliters is the metric unit to use for the capacity of a thimble.
Capacity isn't a unit it is just a term that means how much a container holds. You can have metric units of capacity, such as Litres and Millilitres.
Metric
A millimeter is a unit of length, not a unit of volume or capacity. Perhaps you mean a cubic millimeter.
A litre is a unit of volume.
The unit is a litre.