Can my sister or my job apply for permanent residence for me after marriage based conditional green card?

Assuming the situation is that you obtained your conditional green card by way of marriage to a US Citizen or Legal Permanent Resident, you should look at page 3, part 3 of the I-751 to see if you qualify for any of the acceptable reasons for waiver of filing jointly with your spouse.

If your spouse does not want to help you remove the conditions from your green card, the law provides for several ways that you can remove the conditions alone. The general rule is that you must file a joint petition to remove conditions but if the following situations apply then you may file alone: 1)divorced (must show marriage was bona fide), 2) you were battered by spouse, or 3) extreme hardship would occur if you were removed from the u.s. if your sister is a U.S. Citizen then she may file for you but a visa will not be available to you until the next 10-12 years. Employer may file for you as well. However, I recommend that you consult with a qualified immigration attorney to discuss the facts concerning your conditional green card and whether you may file without spouse. Good Luck

Perhaps....was there undue hardship................

It may be possible for a separate petition by sister it employer. The better means to proceed may be in filing the petition to remove conditions without filing a joint petition. If the marriage was entered into in good faith see an immigration attorney.