Can you know the sex of your baby at 11 weeks with a regular ultrasound? Or if have to be a 3d or 4d? I have a friend that claim to be pregnant, and told me that's she is 11 weeks and already know what she's having. I have kids and as far I know 11 weeks

It . It is not possible to know the sex of your baby at 11 weeks because the genitalia of the fetus have not formed. Typically between 17-21 weeks, the gender of your baby can be seen via ultrasound.
No. Determining the sex of a child is best done between 18-22 weeks. Although there is development that occurs before then, it can be difficult to definitely determine sex prior to that point.