Here, 'surely' is the correct option as it is used to show that you are almost certain of what you are saying and want other people to agree with you. Here, it is very certain that 'life without work is meaningless.'
'Hardly' as an adverb is incorrect as it is used to suggest that something is unlikely or unreasonable or that somebody is silly for saying or doing something.
'Almost' as an adverb implies not quite.
'Only' as an adjective is incorrect as it is used to say that somebody/something is the best and you would not choose any other.