Assuming your hunting in Iowa, doesn't seem like to much gray area to me.
“Trespass” means entering property with- out the express permission of the owner, les- see or person in lawful possession, with the in- tent to commit a public offense; to use, remove therefrom, alter, damage, harass, or place anything animate or inanimate, or to hunt, fish or trap on the property. The term trespass does not mean entering the right-of-way of a public road or highway. Railroad right-of-ways are considered private property.
This paragraph does not prohibit the un- armed pursuit of game or furbearing animals lawfully injured or killed which come to rest on or escape to the property of another.
I would alway consult the Iowa code and/or the game warden of the area in question before acting on information from a Internet forum. I probably wouldn't even bring a pocket knife just to avoid the possibility of it being considered a weapon.
My one question to this situation is can a friend who didn't shoot the deer legally help you track or only the hunter?
It common practice to check with the landowner for safety and respect. If it's after shooting hours, within sight from the property, and I'm way out in the woods I'll grab the deer quick. Unfortunately it's abused to push deer sometimes.