So this is all guess work bu i have up with this for NBT

NBTTagCompound nbt = new NBTTagCompound();
                        nbt.setString("modle", "blockDiamond");
                        nbt.setString("owner",player.getDisplayNameString());
                        nbt.setString("date", String.format("%1$td/%1$tm/%1$tY", System.currentTimeMillis()));
                        ItemStack item= moddedAchievement.item();
                        item= new ItemStack(item.getItem(), item.stackSize, iem.getMetadata(), nbt);

This is obviously wrong but this is my first attempt of giving a item stack NBT

 

I have also tire the write to nbt method with no luck

 

away the item stack is added to player like this

player.inventory.addItemStackToInventory(item)

if it is important all this is only happening server side

 

Do not use the

ItemStack(Item, int, int, NBTTagCompound)

constructor, the fourth argument is for the capability data rather than the stack's compound tag. Use

ItemStack#setTagCompound

to set the stack's compound tag.