The practice of "corresponding author" only exists in some scientific fields, while other fields make no such distinction.
In general "corresponding author" is a distinction that strongly differentiates author roles, such that some authors are "workers" and others are "bosses", with the biggest "boss" being the corresponding author. It typically shows up in more experimental fields, such as biomedicine, where a single PI may have an army of grad students and postdocs acting as lab techs and a paper can easily have a dozen or more authors, some of whom made minimal intellectual contribution. It would make no sense to write to an author who knows little about the paper, and thus the notion of "corresponding author" can make a lot of sense for such a collaboration.
Other fields, particularly more theoretical and mathematical ones, explicitly reject this distinction. Some even reject the notion of significance in author order and expect authors to be listed alphabetically. For these fields, the collaborations tend to be much smaller and much more intellectually balanced. The notion of a "corresponding author" makes no sense for such a collaboration.
IEEE's breadth includes communities at both extremes of these practices, and thus if you do not see a corresponding author, you should assume that the paper comes from a community that does not make such a distinction.
Bottom line: if you don't see a "corresponding author" you can write to any of the authors with an email address listed or, better yet, cc the full collaboration.