difference between tanoshiku and tanoshii ?
o-sake o nondara,tanoshiku narimasu ka.

why here tanoshiku instead of tanoshii ?

Question

difference between tanoshiku and tanoshii ?
o-sake o nondara,tanoshiku narimasu ka.
 
why here tanoshiku instead of tanoshii ?

Answer

Tanoshiku is a conjugation of tanoshii and you use it when you want to link tanoshii to another verb. In the case of your sentence it was the verb "naru".

e.g tanoshiku naru/narimasu

Answer

tanoshii = adjective
tanoshiku = adverb