I did some further research and see that you're asking about the father Ferdinand and not sone Ferdinand's marriage
1900 Breckon, Pierce, Washington Ferdinand Mankowsky, b. Germany April 1843, marr 16 yrs, immigrated 1867, naturalized, farmer. Catherine, wife, b. Germany April 1858, imm 1883. Amal Mankowsky, stepson, b. Germany Dec 1877, imm 1883, blind. Ferdinand Mankowsky, b. WA Aug 1885. Mary A. Mankowsky, b. WA July 1887. Caroline G. Mankowsky, b. WA Dec 1890.
Looks like Ferdianand and Catherine married about 1884. I checked the Washington State Digital Archives and didn't find their marriage info. However, I don't know if all the records are in this system or not.
You could contact the Pierce County Auditor, www.co.pierce.wa.us/ and ask if they have any marriage licenses back to 1884. Successful Searching!