Can I call a function of a shell script from another shell script?

Refactor your second.sh script like this:

func1 {
   fun="$1"
   book="$2"
   printf "func=%s,book=%s\n" "$fun" "$book"
}

func2 {
   fun2="$1"
   book2="$2"
   printf "func2=%s,book2=%s\n" "$fun2" "$book2"
}

And then call these functions from script first.sh like this:

source ./second.sh
func1 love horror
func2 ball mystery

OUTPUT:

func=love,book=horror
func2=ball,book2=mystery

You can't directly call a function in another shell script.

You can move your function definitions into a separate file and then load them into your script using the . command, like this:

. /path/to/functions.sh

This will interpret functions.sh as if it's content were actually present in your file at this point. This is a common mechanism for implementing shared libraries of shell functions.