Please note that, though PAN card of, either you or your sponsor, is (almost?) always required to send tuition fees abroad. Tax Clearance Certificate is required only in the case of some countries and in certain cases, and you need to produce it when the embassy specifically asks for it. For example, if you have applied for the residence permit to Finland, and to fulfill the means of support requirement, you have shown your or your sponsors' (who work in Nepal) salary, Finnish Immigration Service usually asks for the Tax Clearance Certificate from Inland Revenue Department. If it is not required for the country you are applying to, do not let it puzzle you.
Now, for the Tax Clearance Certificate of your salary, first you need to make sure that your taxes have been regularly paid from your salary. Sometimes your employer might not have paid your taxes for the fiscal year, and nothing will be shown on the Tax Clearance Certificate. In that case, you need to first contact the person responsible for paying the taxes, in your office, probably the accountant, and make sure if the applicable taxes have been paid. If those have not been paid, request the accountant to pay it so that the amount of taxes paid will be shown in your Tax Clearance Report from Inland Revenue Department(IRD). IRD will issue the document in Nepali, and you can have it translated into English from any registered notary public office. I had mine translated at NPR 300, but the charges may vary; also you can bargain to see if you can bring the price down.