Many journals do not provide DOIs for articles. When no DOI is on an article, you do not need to include it in your citation. Not every journal uses DOIs because they have to pay to register the numbers.
If it's an online source, and you don't have the DOI, go ahead and use the URL from where you found it.
Example:
Kim, H. (2018). Art in the first and second wave feminist movements. The EXP Journal, 2, 38-52. Retrieved from http://icfleaders.org/wp-content/uploads/2018/09/EXP-Journal-07-2018.pdf#page=38
Call (360) 650-3219
Text (360) 797-5910
Tweet @WWULibraries
Call (360) 650-3219
Text 
Tweet 
Facebook