The Halachah is that the Shaliach must either see the Sofer write the first line of the Get (according to Rashi/Tosfos he must see the line that contains his and her names), or hear the Sofer preparing the Klaf and the Kulmus Lishemah, or hear the Sofer writing the beginning of the Get Lishemah (Shulchan Aruch EH 142:15 and Beis Shmuel). However, regarding the signatures, he must watch both witnesses signing the Get from start to finish (ibid). We are stricter about the signatures than the writing of the Get because the Halachah follows the opinion of Rava that "b'Fanai Nichtav b'Fanai Nechtam" was instituted for the purpose of Kiyum Shtaros (validating the Get, which is done by validating the signatures) and the only reason he needs to say "b'Fanai Nichtav" is so that we don't make the mistake that Kiyum Shtaros can normally be done with one person instead of two (Prishah, ibid).

Kol Tuv,

Yonasan Sigler

I assume that you are referring to the Gemara's question 'ha Lo Kachazi Lei?'

Seeing as he is going to testify that the Get was written and sealed in his presence, then that is what he ought to see.

Be'Virchas Kol Tuv.

Eliezer Chrysler