how to charge ipad without a cable

Sorry no.

Since the charging port might be dirty, I suggest that you make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

iPad does not support inductive charging. If the charging port is damaged, your iPad will require repair.

In the first instance, you would be well advised to seek assistance from the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP), where your iPad can be assessed by Apple’s technicians.

Genius Bar Reservation and Apple Support Options - Apple