Hey there. Your portfolio should be thought of as a whole. My allocations on my portfolio are based across all accounts. Lets say I have a $100,000 account and hold the same stock in all 3 accounts at $2500 each account.
My allocation would be $2500 x 3 = $7500, or 7.5%.
Allocations should simply be the amount of exposure you have to a particular asset relative to the entire size of your investment portfolio.
Another example would be say you have a $1M portfolio, $500k being in fixed income. If you own $50k of a particular stock, it would be pretty easy to think your allocation is 10%, as you own $500k in stocks and $50k in this particular stock. However, once you factor in your fixed income, it is actually 5%.