A sixth level duskblade channels shocking grasp and misses his attack. I believe he still holds the charge to his next round. Now would he be able to take a full attack action with the shocking grasp being discharged when he hits? Casting the spell and channeling it is a standard action, but now that he is holding the spell why couldn't he use a full attack?
Yes, he can full attack with a spell on his blade.
Arcane Channeling class feature uses standard touch spell rules with some exceptions. While there are exceptions, they change nothing in how one holds the charge after the initial casting. So said Duskblade may use Full Attack action if he already is holding the charge, but the spell will still discharge after a single hit, so his remaining attacks are just regular melee attacks.
In general, all characters may do just that by first acquiring a charge (casting a touch spell without attacking or missing on initial attack) and than full atacking unarmed. They may even full attack with touch attacks (when first hit is scored, the spell discharges, and remaining attacks are abandoned) which usually is a better option for a non-gish.
You can't Full Attack with Arcane Channeling, and having the spell affect all targets, until 13th level.
There are some inaccurate assumptions in your question.
- You aren't holding the charge. You already "cast" the spell whenever you channeled it through your weapon.
- Shocking Grasp doesn't discharge until you hit someone. As soon as you hit someone, it discharges.
- You can't full attack with arcane channeling until you reach level 13. There is no way around that using the information provided by the class.
- Can you full attack and have a spell affect the first target hit prior to level 13? Absolutely.
Arcane Channeling at 3rd level - 12th level:
If the melee attack is successful, the attack deals damage normally; then the effect of the spell is resolved.
Arcane Channeling at 13th level on up:
The spell affects each target you hit in melee combat that round.
You can see by the text that prior to level 13, the spell will dissipate on the first person you successfully attack. After level 13, the spell will dissipate after a hitting whomever during that round.
Note: If you were asking if Arcane Channeling would prevent iterative attacks, it doesn't do that. Only the spell would or would not affect targets of your full round attack action depending on level.