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.