To read a boolean property (i.e. a property which is either "on" or "off"), use if property.
To read the value of a property, use the following syntax within any parameter:
#object name:property#
For example, if you have an object called "cod" and it has a "smellstrength" property, you could read this in an msg command using:
msg <The cod has a smell strength rating of #cod:smellstrength#.>
#(variable name):property#
If the object name needs to be a variable - for example, you want to add a SMELL command that the player can use to get the smell strength of any object - put the variable name in brackets as the object name. For example:
command <smell #@thing#> {
msg <The #@thing# has a smell strength rating of #(thing):smellstrength#.>
}