Unfortunately, there is no escape character in XPath, so you have to use the concat function.
Selenium2Library has a function to handle this, which I used to get a XPath. Try:
//span[text()=concat('I have question and if you answer as ', "'", 'yes', "'", ' you will proceed else will "discontinue" from screen')]
${utils}= Evaluate Selenium2Library.utils Selenium2Library
${escaped xpath}= Call Method ${utils} escape_xpath_value I have question and if you answer as 'yes' you will proceed else will "discontinue" from screen
Kevin