I don't understand what your requirements exactly are. As far as I understand your prictures -whose shows your structure- the marked tags are a part of full path from others. So there is no other way. May be the keyword 'contains' allows you to avoid der percent signs. My above query would looks like:
SELECT * FROM [dam:AssetContent] AS page WHERE ISDESCENDANTNODE(page ,"/search/in/path")
AND NOT (Contains(page.[cq:tags], 'dsc:keywords') or Contains(page.[cq:tags], 'dsc:device'))
The query builder pendant for my both queries is:
path=/content/dam/xxx
1_group.1_property=jcr:primaryType
1_group.1_property.value=dam:AssetContent
2_group.1_property=cq:tags
2_group.1_property.value=dsc:keywords%
2_group.1_property.operation=like
2_group.2_property=cq:tags
2_group.2_property.value=dsc:devices%
2_group.2_property.operation=like
2_group.p.or=true
2_group.p.not=true
orderby=path