Intro
Ahmadi’s are cherry pickers, they cherry Al-Zamakhshari only when one of his comments agrees with Ahmadiyya thought.  They use him as they deny the “substitution-theory” and for the alleged death of Esa (As), however, that is where it ends, since everything else that he wrote disproves Ahmadiyya.  In terms of prophethood, we have a few references from Lahori-Ahmadi books wherein they have quoted Zamakhshari and thus ripped the Qadiani’s and their level of academic dishonesty.

Zamakhshari on prophethood fully explained
Zamakhshari, no doubt, stated that khatam means a seal, but he has not denied that it also means last.  After stating the meaning of khatam as a seal it has been mentioned clearly – akhiru-hum la yanba’u aha-dum ba’duhu, that is, the last prophet after whom there would be no prophet. Thus in Kashshaf by Zamakhshari, although khatam means a seal, nevertheless, Khatam an-Nabiyyin according to him decidedly means the ‘Last of the Prophets’ as has been mentioned at the same place: fa-in qultakaifa kana akhirul anbiya-o; that is, if he had said so, then how is he the ‘Last of the Prophets’?  He also accepts the reading of khatam (with fatha on ta) and states distinctly: inna-hum bihi khutimu nabiyyin-fa –huwa kal khatimi wat-tabi-i ‘la-hum, that is, prophets have come to an end with him (the Holy Prophet), thus he is like a seal and signet for them. Because when a seal is set on something it means that nothing can enter therein. Whatever meaning is given to the Hadith about the Holy Prophet being the last brick of the palace of prophethood is applicable to the word seal.  Then he writes wa man zahaba ila anna al-nubuwwata mukhtasabatun la yanqatiu’…. fa huwa zindiqun yajibu qatalahu, that is, and he who holds the belief that prophethood could be acquired and has not been terminated is a heretic and deserves death.

Links and Related Essays
http://aaiil.org/text/books/mali/lastprophetmuhammad/ch1questionprophethoodmirzamahmudahmad_pf.shtml