Try this:
path=/content/hr/stock/ubs
1_property=@jcr:content/cq:lastModified
1_property.operation=exists
1_property.value=false
p.limit= -1
property.operation can take one of the following values while using the property predicate evaluator.
equals for an exact match.
unequals
like partial matching
not for no match
exists for existence match
In your case to search for all nodes where the property `@jcr:content/cq:lastModified` doesn't exist.