I am making a map in 1.12.2, I want to make it so when you trow a specific item on the ground there will be a pillar placed on those coordinates. Can someone help me? (I already have the dropping system, I only need the pillar to be teleported)
It's very similar to the 1.13+ variant, just with different syntax:
/execute @e[type=item,<whatever other conditions>] ~ ~ ~ clone <lower pillar coordinates> <higher pillar coordinates> ~ ~ ~
<whatever other coordinates> with the conditions that you have already figured out (scoreboard or whatever),
<lower pillar coordinates> with the lowest X, Y and Z coordinates of the pre-built structure (for example
123 456 789) and
<higher pillar coordinates> with the highest ones (for example
133 466 799 for an 11×11×11 pillar).