I would recommend him to Wat Phra Kaew, the Temple of the Emerald Buddha is perfectly because of the importance of Thailand and is a beautiful place.
And I would suggest he eat spicy prawn soup Tom yum Kung, because Tom yum Kung is thai food and has delicious
And another place that I would recommend he go to Ayutthaya because Ayutthaya is a important history point of Thailand, and is also a place with many temples.