The reading おうか uses the standard on'yomi for both 謳 (おう) and 歌 (か). 謳 means to sing praises. Wrong readings like おうが mispronounce 歌, and おんか mispronounce 謳. It means to celebrate something with great enthusiasm, often by expressing joy or praise, or to enjoy a prosperous period to the fullest.

謳 (おう) も 歌 (か) も標準的な音読み。歌い上げて褒め称えるイメージ。恵まれた状況を存分に楽しみ、喜びを表すことです。