your question is not 100% clear and readable. Assuming that you want to ask
"I have a WordPress blog that is still currently on the WordPress domain, but when i add a new domain of my own, will people who visit the old domain will get forwarded to my new one?"
The answer is, nothing automatically will come to your new domain unless and until you tell your visitors about your new web address. Here visitors includes humans and crawlers.
Telling your visitors about your new web address will be a tired approach. So here you need to perform redirection. You will have to redirect your old domain address to new domain address so that crawlers and humans, both lands on your new domain without loosing your existing SEO efforts.
There are many redirection rules. But to preserve your existing efforts you need to perform Permanent Redirection called 301 redirects.
Here is a guide to understand the same in better way and to perform this redirection
https://www.wantextra.com/how-to-do-...ress-htaccess/