Esta é uma pergunta comum e duplicada. Você pode usar abaixo:adicione "OR @parameter is null" a todos os seus critérios
Select tblQuickRegister.memberId , tblUserLogin.lastLogin , tblQuickRegister.dob,tblPhysicalAttributes.height,
tblHomeTruth.religion, tblEducation.highestQualification , tblOccupation.occupation, tblPicture.profilePic1
from tblQuickRegister full outer join tblUserLogin on tblQuickRegister.memberId = tblUserLogin.memberId
full outer join tblPhysicalAttributes on tblQuickRegister.memberId = tblPhysicalAttributes.memberId
full outer join tblHomeTruth on tblQuickRegister.memberId = tblHomeTruth.memberId
full outer join tblEducation on tblQuickRegister.memberId = tblEducation.memberId
full outer join tblOccupation on tblQuickRegister.memberId = tblOccupation.memberId
full outer join tblPicture on tblQuickRegister.memberId = tblPicture.memberId
full outer join tblMaritalStatus on tblQuickRegister.memberId = tblMaritalStatus.memberId
full outer join tblContact on tblQuickRegister.memberId = tblContact.memberId
where
(tblQuickRegister.sex = @sex or @sex is null)
And (tblMaritalStatus.maritalStatus = @maritalStatus or @maritalStatus is null)
And ((DATEDIFF(DAY,Convert(date,tblQuickRegister.dob),getdate())/365 >= @minage) or @minage is null)
And ((DATEDIFF(DAY,Convert(date,tblQuickRegister.dob),getdate())/365 <= @maxage) or @maxage is null)
And (tblContact.[state] = @state or @state is null)
And (tblContact.city = @city or @city is null)
