Grb (Arbach), but this epithet of ʿṯtr is normally preceded by the pronoun ḏ. If the word is really an epithet of ʿṯtr, the most probable restoration - on the basis of the lenght of the gap - should be Ḥgr.
According to the editors, the text comes from Nashshān, on the basis of the divine epithet they restore (Grb). However, this reading is very uncertain and it is possible that the text originated from Kamna (see the textual remark on the reading Ḥgr).
Arbach, Mounir and Audouin, Rémy 2007. Collection of Epigraphic and Archaeological Artifacts from al-Jawf Sites. Ṣanʿâʾ National Museum. 2. Ṣanʿāʾ: UNESCO-SFD / Ṣanʿāʾ: National Museum. [Text in English and Arabic]
Rossi 2022: 241, 480, fig. 46
Rossi, Irene 2022. The city-states of the Jawf at the dawn of Ancient South Arabian history (8th-6th centuries BCE). II. Corpus of the inscriptions. (Arabia Antica, 17/2). Roma: «L'Erma» di Bretschneider.