This article is from the The Terminator FAQ, by Karsten A. Loepelmann firstname.lastname@example.org with numerous contributions by others.
The Terminator told John that the T-1000 could replicate "anything it samples
by physical contact." It appears that the T-1000 can use a medium to do this
without actually touching the victim's skin. In scene where the T-1000
mimicked the guard at the Pescadero State Hospital, the only contact was when
the guard walked on the floor, where the medium was the soles of the shoes
guard was wearing.
JC, in the T2 SE supplements, explains that the T-1000 has the ability to
sample things that it touches at a "fantastic level." In a scene cut from the
theatrical release, the T-1000, after killing John's foster parents, searches
for clues to John's whereabouts. It touches the walls, and immediately
determines that there is a cache (of tapes and letters from Sarah, as it
out) behind a poster in John's room (see section 1.2.2).