I need to fix a 10 k potentiometer on expression pedal on model yamaha EL100. model number of potentiometrr not known. pl advice which one can fit.

Generically, for this kind of part, search Google images for one that looks the same, check the dia of the thread, usually 6mm (4mm is common) and then all you have to find out is weather the part is linear or log,
If the pedal passes audio it will be log. If it changes a control voltage then it could be either. Measure from end to end and then measure from one end to the wiper. If it is half (roughly) the value halfway round then the pot is linear. if not then it is log.
Try CPC, yes this a very long address!!!
http://cpc.farnell.com/jsp/search/browse.jsp?N=411+207396+110135389&No=0&getResults=true&appliedparametrics=true&locale=en_CC&divisionLocale=en_CC&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=411+207396&mm=1002553'',&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D411%2B207396%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_CC%26divisionLocale%3Den_CC%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D411%2B207396
All the best Chris.