can i put a skoda fabia engine on a skoda felicia 99 glx

yeah possibly, which one?

1.4 16v

1.4 16v gasoline

that would be a drive-by-wire one with fairly complicated wiring etc, i would suggest that if you have to ask if it's possible then you wont have the necessary skillls to graft it in anyhow... a far easier swap is a 16v engine from a 6n polo which is also 100bhp... somebody on here has written a thread on it if you use the search function