You will find the maximum weight the car can tow on the registration document and on a plate on the car. If you have the handbook it will also be in there.
The maximum weight a car is type approved to tow is not on any plate on a car. It should be on the towbar assembly, but if you are looking at a car without an EU compliant tow bar already fitted then its not given.
The car will have a weight plate (see your cars drivers manual for details of its location) the plate gives four values:
the Gross Train Weight, (GTW)
Gross Vehicle Weight, (GVW also its MAM)
and the maximum axle load limits for the tow vehicle.
The difference between the GTW and GVW gives the maximum towed weight permitted when the car is
fully laden. Most manufacturers use that figure for the maximum permitted towed weight, but some may give a bigger maximum towed weight limit in the cars specifications subject to the GTW not being exceeded.
All the above is the legal side and must not be exceeded. Caravans are not ideal trailers so the industry suggests (subject to non of teh above being exceeded) that a novice caravanner should tow a caravan not exceeding 0.85 of the tow vehicles kerbweight, and experienced caravanners should tow a caravan not exceed the cars kerbweight.
Good towing is not just about weights, it also needs consideration of how the weight is distributed in the car and trailer. It's also important the car and trailer is maintained in good condition, and the driver drives sensibly, observing road conditions and remembering the extra length and width and how that affects handling. and most important of all watch your speed.