Upvote:2
In Buddhism, the word 'dukkha' is used in three different ways, having three different meanings:
The only 'dukkha' Buddhist enlightenment ends is the 3rd type of dukkha above; which is the dukkha of egoistic attachment.
The residual discomfort of touching the forehead is the unpleasant feeling sensation of the 1st type of dukkha. Eradicating this type of dukkha is not the purpose of Buddhism and not the type of dukkha to be "fully understood", "verified" or "known for certain" ("pariññāta").
When SN 56.11 says dukkha is to be fully understood, this refers to the 3rd type of dukkha:
Now this, bhikkhus, is the noble truth of suffering: birth is suffering, aging is suffering, illness is suffering, death is suffering; union with what is displeasing is suffering; separation from what is pleasing is suffering; not to get what one wants is suffering; in brief, the five aggregates subject to clinging [attachment] are suffering... This noble truth of suffering is to be fully understood (pariññāta).