I'm a postgraduate student, doing a accent perception study, this is my first time using SPSS!

I'm conducting the above tests on my data, where my participants used Likert scales to analyse the personality traits of 2 guises produced by speakers from Devon. Because of this, some of my responses are 'unknown' or sometimes the participants have put 'don't know' as a response. My question is, do responses such as these count as missing values in my data? Also, is there a specific command in SPSS to ensure that you 'exclude cases pairwise' or is it an automatic thing?

Also, In order to set up my data set on SPSS, I have ordered my data in Excel, before I copy it across to SPSS. For each dependent variable, e.g. 'perceived class' I have 4 speakers producing 2 separate guises and I thought the easiest way to ensure that my scores were above 5 for the chi-square for independence test would be to simply add all the scores per participants for each guise, for example, all 4 of participant 1's 'perceived class' scores for the 2 guises etc...

The Psych textbook I'm using suggests a score of 99 or 999 for missing values, so if I put 99 for a missing value in excel and I am adding those scores together, is it going to affect my scores in Excel?