[Solved]-Can't get element-LINQ,C#

your code assumes that <te.te> is a direct child of <lemma>, which it is not. rather, <te.te> is a child of <te>, which is a child of <sense>, which is a child of <lemma>. your code should be adapted like so:

let null_te = query.element("sense").element("te").element("te.te")

for simplicity, you could, as jimmy_keen suggests, use descendants:

let null_te = query.descendants("te.te").firstordefault()