In Pratikraman those lines are part of confession and forgiveness. Touching the ground (bhūmi-sparśa) and then the head (śira-sparśa) is a humble vinay-mudrā with this meaning:

• Touch the ground: I bow to all beings and to the holy path, acknowledging that many of my faults happen through the body while moving and “touching” the world. It is also an asking of forgiveness from countless subtle jīvas that dwell in the earth and are harmed unknowingly.

• Touch the head: I place that humility “on my head,” meaning I accept the discipline of the Āgamas, and I resolve with right understanding to keep my mind pure so the body does not repeat those faults.

Why at “Aho kāyam kāya-samphāsam…” and “jānijjāmi vā avajānijjāmi vā” (often pronounced as you wrote)?

• Those phrases specifically admit bodily contacts/transgressions and faults done knowingly or unknowingly. The gesture matches the words: first acknowledge on earth (body-level), then internalize the resolve in the head (mind-level).

Tradition notes

• Śvetāmbara Pratikraman commonly does this during Iriyāvahiyā/Alochana and Kṣamāpanā; devotees touch the floor with fingertips and then touch the head.
• Digambara Pratikraman and daily vandanā also include bhūmi-sparśa/pañcāṅga praṇām; some place the “dust” upon the head as a sign of utmost humility. Exact spots and timing vary by saṅgh, but the intent is the same.

For a simple overview of Pratikraman and these parts, see: and