Hello - I work full time time at a company and am also a part time realtor. How do I report the real estate income and related expenses ? Do I need T4A from my brokerage?

Normally the realtor will issue a T4A, though they have until the end of February to issue it.  You may wish to contact the realtor to confirm.  The income from the T4A will be included as part of your self employed statement (T2125), it is part of your tax return. 

If the brokerage does not issue the T4A, shall I just enter the total commission received? If so, is that the commission + HST or shall I report the commission without the HST? I have to pay the HST back to the government so confused on how to report the commission. Thanks.

You will already have reported your HST on the income, and on expenses, on your HST return.  So when filing the business portion of your personal tax return you will include income and expenses without the HST.

So if the T4A show in Box 20, $100,000. and no other box with number;

That $100,000 includes GST 5%

Do I write $100,000 as business income and $5000 as expenses or 

do I write $95,000 as business income.

Thanks