I know of people who tested urine or saliva to monitor ph levels but I did not. I monitored it symptomatically. I could feel when my gut was more acid and it eventually became clear that lung inflammation was directly correlated.

As for blood ph, the body works really hard to keep that within a narrow range. Otherwise, you die. And pretty quickly. The body will strip your bones of calcium to try to keep blood ph stable. If you have an acidity issue, it is best to assume it is systemic rather than localized.