How easy is it to get pregnant with condom and no ejaculation?

Very difficult. If you use condom and have no ejaculation you can not get pregnant as no sperms will enter the vagina.
Rare. It would be rare but the chances aren't zero. Condoms are about 85% effective. Pregnancy can occur without ejaculation. Whenever a penis is inserted into a vagina, there is some chance of pregnancy.