Is UPSC convocation certificate mandatory for UPSC documentation

Unnecessarily you have delayed taking your degree certificate. Once the convocation is over your provisional certificate is invalid. So you have to take degree certificate. If the convocation of the university for the year you passed is not over means provisional certificate is valid. Otherwise your Provisional Certificate is not valid.

You need not wait up to 2020. You can apply before the convocation itself you can apply by paying late fee and penalty fee. Personally you can visit the university and see that you will receive your certificate immediately,
If there is no time you can go with provisional certificate and tell them some valid reason for not taking original certificate and ask them to give some time to produce the original certificate. They may consider.

You should take degree from your University as soon as possible. A provisional certificate is a temporary certificate and it is issued by a university until a permanent degree is issued. It is usually distributed during convocation ceremony. Validity of a provisional degree certificate is 6 months or until university issued a degree certificate.

As almost 10 years have been passed, you can apply for your degree anytime. Don't wait for 2020 convocation. For this you will have to contact to your University's Examination cell for degree certificate. You will have to pay a requiseite fee. You can write to your university and send fee demand draft or visit physically to your university and can collect degree certificate from there. There will be no issue if you are going to collect it now. I myself also collected my degree 2-3 years later due to some reasons.

In job it is necessary to show original degree, but its already been long time has been passed. But still you can go with your provisional certificate and convince them that you had applied for original degree and will submit later. Might be they allow you.

You are utterly confused by saying that convocation - certificate is mandatory during the verification of documents at UPSC. However, it is too late to procure your original degree certificate though you have passed long back ie in the year 2010.
Again to get back your original degree certificate, it is not at all necessary to present yourself in the next convocation to be held in April 2020. This can be done by either of ways, by visiting your university personally and submit the requisite fee by cash or through demand draft and application forwarded by the principal of the college from where you have passed and the other way would be to request the registrar of the university to release your graduation certificate through the registered post at your destination. You will have to send an application indicating your request to send your degree certificate through the registered post for which you need to attach the appropriate demand draft of a bank acceptable to them of an appropriate amount including the charges of its posting. This has to be sent through the registered post with an acknowledgement so as to ensure that it has reached to the university officials. The degree certificate would be despatched to you shortly without you needing to be present in the next convocation.
Your provisional certificate issued in 2010 is no more valid because you have failed to procure your degree certificate in time.

You have to immediately apply for your original degree by sending an application to the registrar office of the university by tendering the requisite fee and hopefully they will be sending it quickly to you. Please preserve a copy of this application with you and also pursue this case with an email to their office and keep a copy of the same also with you as a record. Now a days because of digitisation you may get a quick acknowledgement of your email also and in that case keep a copy of the same with you.

Now you can produce all these documents along with the provisional degree certificate for verification purposes. You have to tell that you will be submitting the original degree certificate also as soon as you get it. Convocation is a formal thing and one has not to wait for the original degree till then. Normally a provisional degree is valid for 6 months only but if you have documents with you which can show that it is still pending with the university and they are delaying it, then you can impress your credentials with the provisional certificate also. Do not worry as in the extreme case your appointment will be made on provisional basis subject to the producing of the original degree certificate within some stipulated time and in that case you can physically go there and get it on priority and submit in the present recruitment.