Denim motorcycle riding jeans have an aramid-based fabric either knitted into the weave of the denim or added as panela that line the inside of the jeans. The most well-known of these fabrics is Kevlar, but there are rival fibers with brand names like Covec and Pekev that do a similar job. If the manufacturer claims they are 'Kevlar motorcycle riding jeans' that means they have been licensede by Kevlar's parent company DuPont because they must have passed the abrasion section of CE-approval.
A few top-end jeans will have full CE-marking, either CE EN 13595-1 Level 1 or the higher Level 2, but they are the fully-lined and bulky versions. A full lining adds a lot of weight and a restrictive feel to the jeans which is at odds with the casual look, and you won't want to walk around in them on the average day in tropical Thailand.
The lighter, more popular jeans have panels of abrasion-resistant materials only in key areas like knees, hips and seat. Remember these jeans are a compromise and will not offer impact protection unless you buy CE-approved jeans with armor, or fit it as an option to non-approved jeans as some have pockets that allow you to add hip or knee protection.
The manufacturer of Pekev fiber claim that their Pekev fiber and fabric is lighter than Kevlar and more UV-resistant, while the manufacturer of Covec reckons that their Covec fibers are lighter too, wick away moisture and breathe well so you won't boil wearing it in Thai tropical weather.
The vulnerable areas are knees, hips, thighs and seat of the pants and I'd suggest coverage for knees, hips and seat as a bare minimum. Look out for optional armor pockets to add extra protection.