A goal statement is also known as a statement of purpose’ or personal statement and is a personal description of your long-term professional goals.
here, give this in the context of what you intend to do with your DBA degree.
I got help to choose my topic "Investigating Environmental Management Accounting’s Impact on SME Sustainability in Mongolia: An Exploratory Study" So it should include about it and mention about my Accounting background and goal that I want to grow in my career to Senior level etc.
1 or 2 pages are fine.