Does the tear aid A work on ordinary clothing?
I...don't know!
I've had stellar luck with TearAid on outdoorsy stuff like tent flies, panniers, even rain jackets and such but in all cases, nylon-based materials and things that would not get the sort of continuous flexing of a trousers knee.
By rounding/radiusing the corners of my TearAid patches, I've not had them lift, but again this was on nylony fabrics.
TearAid is stretchy to a degree and seems to remain sort of rubbery to the touch. It can be pulled to conform a little and if it is clamped till it cures, seems to stay that way afterwards.
SD, where your trousers are waterproof/breathable, TearAid might well work...or it might not. I think the best chance for success will come if the fabric surface is smooth and regular and petroleum based and does not "fuzz". I would say the chances for success on cotton would be very low.
Nothing definitive, but I want to follow the dictum "Primum non nocere" here...first do no harm. Not having tried it, I think you'll have to experiment. I'd try Tear-Aid first on an inconspicuous part of your trousers, say inside the hem at the lowermost part of the leg, where it is cuffed over. That way, if it did not work it would be neither a structural nor aesthetic failure.
Best,
Dan.