Verified answer

You can only pick up the Sticky Detonator when playing online. You can't unlock it for your loadouts.

Why do you have multiple questions about ordinance weapons being used as loadout weapons? O_o

The sticky detonator is an ordinance weapon. It can't be unlocked as a loadout weapon. If you want a higher chance of getting it in games that allow ordinance drops to be called in, you can use the perks that fill up your Ordinance faster, and that let you call in a new ordinance selection if you don't like your choices.

Impossible, the Stick Detonator isn't an unlockable loadout weapon.

I would choose either the Assault Rifle or the DMR for your main weapon. Secondary, since you're not that good at weapons, I would choose the Plasma Pistol (to take down enemy shields but also to help teammates either take down or acquire vehicles).

Sadly you can't unlock it you have to find it on a map