This dua is usually recited on the month of Ramadhan, during the night prayers aka Taraweeh. It is usually recited in between the prayers, some mosques recite it loudly after every 2 Rakkahs(Prayer ritual of 2 bows and 2 prostrations), some after every 4, some after every 10 and some none at all. However, in Tanzania most mosques say this dua in between prayers throughout Ramadhan.
I leave you with the Hadith Below:
A’isha (May Allah be pleased with her) asked the Prophet(peace be upon him), “If I knew which night is Laylat al-Qadr (the Night of Power), what should I say during it?” The Prophet told her to say:
Allahumma innaka ‘afuwwun tuhibul ‘afwa fa’fu ‘anni.
“O Allah, truly You are all-Pardoning, You love to Pardon, so Pardon me.” [Tirmidhi]