How can one get rid of urine drops absorbed by clothes, taking into account that this occurs at work or on the road?

Doubt about the emission of impurities does not necessitate purification. The default is that impurities have not exited unless there is certain conviction. When the emission of urine is confirmed, the affected part of the garment must be washed and istinja' performed for prayer. If the location of the urine on the garment is hidden, then what ensures certainty of the removal of the impurity must be washed. Some scholars, like Ibn Taymiyyah, hold that a strong presumption of the removal of impurity is sufficient.