You don't know I can finish the work by myself,do you 还是 can

do you
解析：本题考察的是反意疑问句的附加部分。
一般情况下,主从复合句的反意疑问句附加部分看主句,但是,当陈述部分含I think (believe ,suppose…)that…结构时,其反意疑问句须与从句的主、谓语保持一致,注意主句的主语必须是第一人称。
此题中,you don't know 为主句,I can finish the work by myself为宾语从句,因主句主语为第二人称you ,所以反意疑问句附加部分看主句,不看从句,故为do you。
如：I don’t think he will come, will he?（主句为I don't think, 看从句）