Noun, する verb, and の adjective
こうどく
全アメリカ人がTofuguのニュースレターを購読しているという噂が、日本中に広まった。
The rumor that all American people subscribe to the Tofugu news letter spread throughout Japan.
A subscription has been read. Each magazine that comes in you read. This is your subscription.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. The on'yomi for 読 (どく) is the same as the reading in 読者. In case you forgot, think about how you just got a subscription to dock (どく) magazine. It's all about docks and dock related things. How exciting.