Mark Knopfler doesn't solely use the technique known as "flat picking", although I have seen him use a pick at times.

He plays "fingerstyle" mainly and will simultaneously pluck several strings which are not adjacent (I challenge any player to do that with just a pick).

Hybrid picking is a similar technique which he also uses, which is where you use a pick and picking-hand fingers to pluck strings.

Sorry, but if you want to play like him one day, then fingerstyle is pretty much the only route. You will also need to be comfortable using a whammy bar and wah pedal, along with reverb and delay, if you're after a similar sound.