What type of motor oil for Suzuki drz400?

The manual says use 10W40. If this is not available a 15W40 or a 20W50 will do fine.

The thing to be careful of are the oils desgined for cars contain numerous additives that are bad for bikes, 'high-milage' oils will place unwanted chemicals in your engine and lead to clutch-slippage and other problems.

Rather get a motorcycle specific oil, or get one that you know is additive free.

Also, change it more often than the manual says, rather do it every 3000 or 4000kms, depending how hard you ride. Be sure to put in an extra 200ml when you change the oil filter.