The Sunnah at عرفات is to combine Dhuhr and Asr نمازs at the time of Dhuhr (early combination, or jam' taqdim). Both نمازs are shortened to 2 rak'ahs each since the حاجی is considered a traveler. نبی کریم (صلی اللہ علیہ وسلم) performed them with one adhan and two iqamas — meaning one call to نماز is given, then Dhuhr is prayed with its own iqama, followed immediately by Asr with its own iqama. No voluntary نمازs (Sunnah نمازs) are prayed between them.
This combining serves an important practical purpose: it frees up the entire afternoon from after the نمازs until sunset for uninterrupted دعا, dhikr, and worship — the core purpose of the Day of عرفات. The afternoon hours are the most precious time of the entire حج and should not be interrupted by waiting for the Asr نماز time.
Regarding who should combine: the majority of scholars say all حجاج at عرفات combine, even residents of مکہ مکرمہ who are not technically travelers. The combining is specifically linked to the حج ritual at عرفات, not just to the traveler's concession. The same principle applies at مزدلفہ, where Maghrib and Isha are combined at Isha time (jam' ta'khir — delayed combination). After the combined نماز at عرفات, face the Qiblah, raise your hands, and dedicate yourself fully to دعا.