That written, the thoughts and feelings - often referred to as meaning - a photograph touches in a viewer is intrisically subjective since what a viewer receives from a photograph is, in most cases, primarily determined by what a viewer brings to his/her viewing experience. While, without a doubt, a photograph's visual content influences a viewer's eye and sensibilities, it is the viewer's expectations, experience, prejudices and his/her willingness to fully engage the photograph with an open mind that ultimately determine how a photograph "speaks" to him/her.
iMo, the best manner in which a viewer can expand his/her ability to "listen" to / "read" a photograph is to make a concerted effort to view as many photographs as possible to include as many photographic genres as possible. iMo, original photographic prints (and their close relative - high quality print reproductions in photo books) is the best / richest vehicle for expanding one's understanding of visual language. It is also Mo that learning how to "read" a photograph will be of great benefit to a picture maker inasmuch as understanding the visual lanuage to be found in a photograph (made by others) will help that picture maker with the use of that language his/her own picture making.
FYI, one of the best all-in-one-place resources for viewing a wide range of photographic genres (albeit virtual on a computer monitor) can be found on the Lenscratch Online Magazine resource page. And, surprise surprise, my favorite resource on that page is Square Magazine.