How can I connect a CT clamp (AC Current sensor) to a multimeter?
This is a transformer - a CT with just a clamp (probably a bidirectional TVS) and no load resistor so you will need to supply a burden resistor in order to get a usable reading. 



In the article you linked, 22\$\Omega\$ was used, and you can use something similar, such as 20.0\$\Omega\$ 1%. The output AC voltage will be proportional to the burden resistor up to some value. 20 ohms should be safe. You could also use the AC amperes range of your meter, provided you know that the input resistance is low enough and thus avoid using the resistor. Often AC voltage ranges are a bit more accurate. 

The transformer will supply an output current which is related to the input current by the transformer turns ratio, provided the output voltage is not too high.