Stocks and mutual fund investments are assets. If your business buys and sells then you have purchased an asset to hold. Purchase price plus any fees. Never adjust value (basis) due to market fluctuations. QB is not designed to be a market tracker.
When you sell your receipt minus fees, minus book value of stock is your capital gain. Depends on your country laws, but here 1 year or less held is short term gain taxable at an individual's marginal tax rate. Longer than 1 year is long term capital gain with a different flat rate of taxation on the gain.
An example: al in US dollars: I buy 100 shares of Tata Motors (TTM on NYSE) at $22.15 through eTrade but I am a slow investor, less than 30 transactions per quarter, $6.95 per transaction (4,95 if over 30) My cost for these shares is 2215+6.95= $2221.95
Say it goes up to $25 and i sell, I get $2500-$6.95 or $2493.05 less my basis of $2221.95 results in a gain of $271.10 Say it dropped to $20 and I got nervous and sold, I receive $2000 - - $6.95 or $1993.05 a capital loss of $222.90. Neither transaction really results in income or expense but in gain or loss. Length held determines short or long. Tax treatment will determine where to claim and if the loss can even be used to offset other income.
Now, after all that, if this is the business money being invested and the stocks are owned by the business go ahead and run it through your company books. If it is personal investing it has no place in QuickBooks. QuickBooks is not personal finance software