JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout-validation/2.0.3/knockout.validation.min.js"></script>
Gender:
<select data-bind="value: memberType,
                    options: memberTypeSource,
                    optionsText: 'text',
                    optionsValue: 'id',
                    optionsCaption: 'Please select'"></select>
<br />Seeking:
<select data-bind="selectedOptions: seekingTypes,
                    options: memberTypeSource,
                    optionsText: 'text',
                    optionsValue: 'id', validationCore: seekingTypes" 
                    multiple></select>
<br />
<button type="button" data-bind='click: doValidation'>Submit</button>

JavaScript

ko.validation.init();

function isNotUndefined(val) {
    return (typeof val != "undefined");
}

function isArrayNotEmpty(val) {
    return (val.length > 0);
}

var viewModel = function () {
    var self = this;

    self.memberType = ko.observable().extend({
        validation: {
            validator: isNotUndefined,
            message: 'Please select gender'
        }
    });
    self.seekingTypes = ko.observableArray().extend({
        validation: {
            validator: isArrayNotEmpty,
            message: 'At least one option is required'
        }
    });
    self.memberTypeSource = [{
        id: 1,
        text: 'Man'
    }, {
        id: 2,
        text: 'Woman'
    }];
    self.errors = ko.validation.group(self);
    self.doValidation = function () {
        console.log('error count=' + self.errors().length);
        if (self.errors().length == 0) {
            console.log('Yay.');
        } else {
            self.errors.showAllMessages(true);
        }
    };

    return {
        memberType: self.memberType,
        seekingTypes: self.seekingTypes,
        memberTypeSource: self.memberTypeSource,
        errors: self.errors,
        doValidation: self.doValidation,

    }
};

//ko.validation.makeBindingHandlerValidatable('selectedOptions');
ko.applyBindings(new viewModel);